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View Full Version : DM Help Well I've gotten myself into a bit of a pickle...



WarKitty
2014-11-18, 05:37 AM
*shoos players off with a broom*




Anyways, here's the situation I've gotten myself into. The players have been asked to investigate a leak. Somehow important military information about the guards on a quarry got out to the wrong people. The players have been told to look for the leak among the traders that enter and exit the city - while they must have an inside source there would have to be a traveler who carries the information. They've been given so far the trade manifests with info on everyone coming and going (helpfully this list isn't too long).

And...yeah, I kind of got myself into this without much thought as to what sort of clues I could give them?

BWR
2014-11-18, 07:03 AM
Sounds like plain old detective work. If the timetables are included this can help. "At Time Y we discovered that the Info had been leaked, and the info was applicable only to Time Period AB, and here is the list of merchants who were here during that time" - which guards were on duty when Merchant X was in town, ask around to see if any potential leaks have ties with traders, visit taverns and inns and ask around if they've seen any of Set X and any of Set Y together, see if there are family connections, debt, etc. Check guard rosters or duty logs to see if everything is in order (no one suddenly taking over someone else's shift without properly logging it, etc.), interview/interrogate guards and anyone who had access to the info to see if their stories are ok, etc.

WarKitty
2014-11-18, 07:18 AM
Sounds like plain old detective work. If the timetables are included this can help. "At Time Y we discovered that the Info had been leaked, and the info was applicable only to Time Period AB, and here is the list of merchants who were here during that time" - which guards were on duty when Merchant X was in town, ask around to see if any potential leaks have ties with traders, visit taverns and inns and ask around if they've seen any of Set X and any of Set Y together, see if there are family connections, debt, etc. Check guard rosters or duty logs to see if everything is in order (no one suddenly taking over someone else's shift without properly logging it, etc.), interview/interrogate guards and anyone who had access to the info to see if their stories are ok, etc.

Trouble is that the guards that we're talking about are (1) not in the place where the leak was, and (2) all dead. We're looking at a leak from the capital city about an outpost, for something that the workers at that outpost didn't even know about. Which is a good deal harder because it also gives you a pretty wide timeframe. You're not looking at ties to guards, but to people like secretaries or servants.

BWR
2014-11-18, 07:40 AM
Trouble is that the guards that we're talking about are (1) not in the place where the leak was, and (2) all dead. We're looking at a leak from the capital city about an outpost, for something that the workers at that outpost didn't even know about. Which is a good deal harder because it also gives you a pretty wide timeframe. You're not looking at ties to guards, but to people like secretaries or servants.

So replace 'guard' with 'anyone who had legal or at least physical access to the info'.
How much authority do the PCs have? What system? What abilities?

WarKitty
2014-11-18, 07:50 AM
So replace 'guard' with 'anyone who had legal or at least physical access to the info'.
How much authority do the PCs have? What system? What abilities?

Standard D&D 3.5, they're level 3, almost 4. Practically no authority but a lot of rogue-y skills. They might not even be allowed to talk to citizens on their own, only outside traders.

Earthwalker
2014-11-18, 10:53 AM
Isn't the SOP for spotting a leak to devide the information up and see what gets out.

Tell Trader 1 - The north wall is weakly defended.
Tell Trader 2 - The South wall is weakly defended
Tell Trader 3 - The East all is weakly defended.
Tell Trader 4 - The West Wall is weakly defended.

Then see what all gets attacked.....

Or change for what works.

If this will not work then I will move to the next plan.

Rama
2014-11-18, 04:39 PM
Since they have trade manifests, and you've directed them to look at merchants, the easiest indicator is probably going to be a discrepancy in the declared merchant cargo. If the dirty merchant is a third party just in it for profit, he's likely also involved in other unsavory activities. Drug smuggling, high tariff items masked by untaxed goods, contraband weaponry/magical items, etc.

Clues for that approach could be a corrupt gateguard (as signified by unusual affluence for one in his position - gold ring, nice new boots, etc) who can be pressured to give up his money source; victims of drug overdose and/or murder by contraband weaponry on the rise; or nervous behavior/histrionic displays of innocence upon questioning.

Alternatively, if the merchant is a front for military agents of a rival nation, he's likely smuggling in other things that would assist in an attack. The first possibility that comes to mind there would be slipping troops into the city, disguised as wagoneers/porters. Once they're within the walls, 'fire' all the employees and let them disperse unremarked into the populace. Rinse and repeat a half dozen times and you could have a nice little strike force accumulated in the city. Then once the main army arrives, they seize a gate and let the troops in.

Clues for this approach could be gleaned commentary that the merchant has unusually high turnover in his staff; shortages in employment (due to the merchant's "old" crew not joining the work force while he's draining the available supply to leave the city again); or observed unusual attributes among the merchant's employ (unusually buff/weapon-scarred/etc for wagon drivers).

Just a few thoughts; hope that helps some.

WarKitty
2014-11-18, 05:12 PM
In a region like this everyone has high turnover, is the thing. And you absolutely cannot allow any more information to be leaked since the place it was about was wiped out and with travel distances you can't really run more tests. Merchants don't live in the city, either, they stay there but they're not part of the city generally.

Edit: That seems to be something people aren't getting. The attack location and the investigation location are not the same. The attack location is gone. Everyone's dead.

Vitruviansquid
2014-11-18, 05:24 PM
Some classic DM magic is to take the players' ideas, have the first one fail, and work to let the second one succeed.

WarKitty
2014-11-18, 05:29 PM
Some classic DM magic is to take the players' ideas, have the first one fail, and work to let the second one succeed.

Yeah, the main concern here is I don't want to end up in a spot where the players are floundering around on who to talk to and where to go and I'm floundering around trying to come up with hints. If they go in an interesting direction I'll take it there, but there's a good chance of them asking my NPC's for ideas.

Rama
2014-11-18, 08:14 PM
Let's try a slightly different angle.

The encampment that was the attack location is gone. But my presumption is that (a) the attackers are still alive, kicking, and (b) are unknown or unconfirmed beyond plausible deniability.

So if those two assumptions are correct, what is their endgame? Wiping this location off the map (again without knowing anything) seems to be more an opening play than the winning move. So with the attack done, from an investigative standpoint I'd think they're more like to uncover what they need through evidence of active operations (Phase II being implemented) rather than what's already happened.

WarKitty
2014-11-18, 08:29 PM
Let's try a slightly different angle.

The encampment that was the attack location is gone. But my presumption is that (a) the attackers are still alive, kicking, and (b) are unknown or unconfirmed beyond plausible deniability.

So if those two assumptions are correct, what is their endgame? Wiping this location off the map (again without knowing anything) seems to be more an opening play than the winning move. So with the attack done, from an investigative standpoint I'd think they're more like to uncover what they need through evidence of active operations (Phase II being implemented) rather than what's already happened.

The attackers are perfectly well known, and the target has obvious strategic value. The question is how the attackers managed to sabotage the fortifications, since they'd have needed inside information to do so.

Basically, we know that a somewhat competent local warlord went to seize a quarry. Given the location of the area, it's probably presumed he did that for the fact that it's a valuable resource if you want anything better than a wooden palisade around there. Seizing skilled workers is likely also in the game plan (yeah I messed up saying the attack location was dead), as well as valuable weaponry that would be given to the guards but not traded out. So that's all pretty up front.

Nevereatcars
2014-11-23, 03:28 AM
Start your next session with "After a long and complicated investigation, you discover that Person X has done Action Y and BBEG is to blame." But only if you really have no idea what to do.

Realms of Chaos
2014-11-26, 10:14 AM
Well, you could always give traders stuff that they shouldn't have been able to have. :smallwink:

Seriously, a trader walking into town with an unusually large supply of stone from the quarry or someone caught trying to sell equipment that the former guards of the destroyed area once knew should raise some gigantic red flags. Whether you're dealing with a traitor who was allowed to live/knew to flee early, an early arrival to the scene who might have spotted something others missed, or a lone survivor traumatized into silence... just having someone clearly out of place seems like the easy way out. Alternately, perhaps the spouse or partner of a treacherous trader has a change of heart and is murdered trying to get a message out to the guard, providing a clue in the process.

If that fails, a single one of the attackers caught within the new location (whether on reconnaissance or using looted treasure to get drunk) might be able to provide a clue if you want to be very blunt about it.

Even within the destroyed site (if the party is able to destroy it), physical evidence may reveal how things have happened. A traitor may have kept missives from the enemy to prove that he or she was an "ally". A destroyed scroll of disguise self, invisibility, suggestion, or clairaudience may also reveal how knowledge may have gotten out. Even a scrying pool and small lock of hair left at a camp site just outside of the quarry could give a good clue.

If you really want to say that 1) nobody other than the attackers was associated with the attack, 2) nobody else who could possibly known what happened is alive, and 3) none of the attackers can be found, 4) there is no physical evidence, then the obvious solution is magic. Have a wizard volunteer a wand of speak with dead that has a limited number of charges. Have the local church, fearing for its followers, raise the money required to raise a single individual from the dead and have the party riddle out who to bring back (I doubt that the raiders stole or destroyed every corpse and the absence or destruction of only certain corpses might be a clue in its own right). Hell, a high priest might elect to cast a single commune spell to pick up information and let the PCs select what questions need to be asked.

If none of THAT works, it's possible that one of the traders will give themselves away, giving you any number of clues. Perhaps the traitor is paranoid and, even in the lack of solid evidence against anyone, tries to place (groundless) blame on other traders repetitively. In conversation, a nervous traitor might not be able to keep his or her story straight or the Sense Motive skill may reveal that he is hiding something. Maybe the traitor doesn't know to quit when he or she is ahead and can be found chatting up guards or buying suspicious scrolls that could be used to gain information.

All that I can say is that you probably don't have a lot of wiggle room to go with as far as this mystery goes so please resist the urge to put in an obligatory red herring. :smallsigh:

Kelb_Panthera
2014-11-26, 02:24 PM
Just because everyone's dead doesn't mean you can't talk to them. Speak with dead is a spell. There's also the possibility of accounting for the important people amongst the dead. If someone's corpse is missing, bam, suspect found.

In any case, here's a neat article on setting up mysteries once you've got one written: http://thealexandrian.net/wordpress/1118/roleplaying-games/three-clue-rule

daremetoidareyo
2014-11-26, 06:16 PM
You need an intermediary between the people the PCs are working for and the attackers. You seem to have decided that this is a long term leak and not a short term technique for a 3rd party that profits from the battle between the aggressors and defenders.

Shapechangers is the cheapest way out.

A jilted lover of a high up official is a fun one though. Maybe a general isn't so tight lipped about decisions with his wife, ooooor *gasp* his mistress, oooor *bigger gasp* his favorite prostitute, who happens to be the favorite prostitute of someone who works for the bad guys.

Sartharina
2014-11-26, 07:36 PM
Work backward. You know what happened... generate clues from that.

Jay R
2014-11-26, 10:34 PM
If you build a scenario with only one solution, then they have to come up with your idea to solve it. But if you build a scenario with no solutions, they have a free rein to invent any6thing they like.

So don't pre-generate clues. That means that they have to guess what you decided. Know what is actually happening to cause the leak. Listen to their ideas, and decide which one works. Then work out (quickly) what clue could be found that way.

WarKitty
2014-11-27, 12:51 AM
Well, you could always give traders stuff that they shouldn't have been able to have. :smallwink:

Seriously, a trader walking into town with an unusually large supply of stone from the quarry or someone caught trying to sell equipment that the former guards of the destroyed area once knew should raise some gigantic red flags. Whether you're dealing with a traitor who was allowed to live/knew to flee early, an early arrival to the scene who might have spotted something others missed, or a lone survivor traumatized into silence... just having someone clearly out of place seems like the easy way out. Alternately, perhaps the spouse or partner of a treacherous trader has a change of heart and is murdered trying to get a message out to the guard, providing a clue in the process.

If that fails, a single one of the attackers caught within the new location (whether on reconnaissance or using looted treasure to get drunk) might be able to provide a clue if you want to be very blunt about it.

Even within the destroyed site (if the party is able to destroy it), physical evidence may reveal how things have happened. A traitor may have kept missives from the enemy to prove that he or she was an "ally". A destroyed scroll of disguise self, invisibility, suggestion, or clairaudience may also reveal how knowledge may have gotten out. Even a scrying pool and small lock of hair left at a camp site just outside of the quarry could give a good clue.

If you really want to say that 1) nobody other than the attackers was associated with the attack, 2) nobody else who could possibly known what happened is alive, and 3) none of the attackers can be found, 4) there is no physical evidence, then the obvious solution is magic. Have a wizard volunteer a wand of speak with dead that has a limited number of charges. Have the local church, fearing for its followers, raise the money required to raise a single individual from the dead and have the party riddle out who to bring back (I doubt that the raiders stole or destroyed every corpse and the absence or destruction of only certain corpses might be a clue in its own right). Hell, a high priest might elect to cast a single commune spell to pick up information and let the PCs select what questions need to be asked.


Well, I don't intend for the site to be destroyed per se. But the idea should be that the physical site of the attack is currently under hostile control and difficult to get into, as well as a good distance away. The players aren't just going to be able to head over there and run around examining the site.

And even if they did I'm not really sure what would be gained from an examination of the site itself. After all, there's no mystery about who attacked the site, or how they did it. And the common soldier wouldn't know where the general gets his information.


If you build a scenario with only one solution, then they have to come up with your idea to solve it. But if you build a scenario with no solutions, they have a free rein to invent anything they like.

So don't pre-generate clues. That means that they have to guess what you decided. Know what is actually happening to cause the leak. Listen to their ideas, and decide which one works. Then work out (quickly) what clue could be found that way.

I don't necessarily need it to be a single-solution problem. What I need are enough details to get them going in some direction. Right now pretty much all I have is:

Warlord A attacked the site
Someone fed them information to be able to get past defenses
That information had to come from the main city
The only people that enter or leave the city are traders (not entirely true but that's what they're told so far)
There's a list of traders that have entered or left recently.

That's too homogenous, there's not enough detail to send the players running off anywhere.


You need an intermediary between the people the PCs are working for and the attackers. You seem to have decided that this is a long term leak and not a short term technique for a 3rd party that profits from the battle between the aggressors and defenders.

Shapechangers is the cheapest way out.

A jilted lover of a high up official is a fun one though. Maybe a general isn't so tight lipped about decisions with his wife, ooooor *gasp* his mistress, oooor *bigger gasp* his favorite prostitute, who happens to be the favorite prostitute of someone who works for the bad guys.

Hmm, I'm kind of liking this. Maybe even make it someone lower down - there's paperwork for everything. And where there's paperwork there's secretaries. A young servant's head filled with promises of exotic riches and a beautiful woman persuades him to copy a few documents in secret. Perhaps a secret tryst is noticed, or a servant going on errands that no one remembers assigning him. One of the traders is exotic, an exceptionally beautiful and secretive sorceress. But why does she have a spellbook she never seems to use?

Sartharina
2014-11-27, 01:23 AM
Warlord A attacked the site
Someone fed them information to be able to get past defenses
That information had to come from the main city
The only people that enter or leave the city are traders (not entirely true but that's what they're told so far)
There's a list of traders that have entered or left recently.

That's too homogenous, there's not enough detail to send the players running off anywhere.You should know who the warlord is, who fed them the information, who that informant is and what he's doing, how he got the information, how he conveyed the information, and what he's been doing otherwise, and all other relevant details.

With all those details, you can reconstruct the 'crime scene', and have clues generated from the actions of the informant, and disperse clues from there.

Jay R
2014-11-27, 09:54 AM
Right now pretty much all I have is:

Warlord A attacked the site
Someone fed them information to be able to get past defenses
That information had to come from the main city
The only people that enter or leave the city are traders (not entirely true but that's what they're told so far)
There's a list of traders that have entered or left recently.

That's too homogenous, there's not enough detail to send the players running off anywhere.

Correct. You don't have any clues to the situation because you haven't written any situation yet. You just have an outline about what kind of situation you might write. You need to invent the situation.

Only when you know who's giving the information, why they are betraying the city, what good they are getting out of it, how the information is carried out of the city, when and where the information is gathered, when and where the information is compiled, how it's recorded, and how the warlord receives it, then the clues with write themselves.

If somebody's getting paid a lot, then he's starting to dress better. If he's been promised he'll rule the city afterwards, he know longer cares what the city council is doing. If he's being paid off with the promise of a particular high-born woman, then he's spending more time near her.

Tolkien could only write clues proving that Wormtongue was betraying Rohan to Saruman because Tolkien knew it was Wormtongue.

Similarly, whoever it is must be in a position to get the information, then get it out to the warlord. His method (homing pigeons, sealed letters delivered by an oblivious merchant, verbal information given to a cooperative merchant, etc. ) leaves a trail - but you can't invent clues to that trail until you know the details of what the trail is.

WarKitty
2014-11-27, 11:12 AM
Correct. You don't have any clues to the situation because you haven't written any situation yet. You just have an outline about what kind of situation you might write. You need to invent the situation.

Only when you know who's giving the information, why they are betraying the city, what good they are getting out of it, how the information is carried out of the city, when and where the information is gathered, when and where the information is compiled, how it's recorded, and how the warlord receives it, then the clues with write themselves.

If somebody's getting paid a lot, then he's starting to dress better. If he's been promised he'll rule the city afterwards, he know longer cares what the city council is doing. If he's being paid off with the promise of a particular high-born woman, then he's spending more time near her.

Tolkien could only write clues proving that Wormtongue was betraying Rohan to Saruman because Tolkien knew it was Wormtongue.

Similarly, whoever it is must be in a position to get the information, then get it out to the warlord. His method (homing pigeons, sealed letters delivered by an oblivious merchant, verbal information given to a cooperative merchant, etc. ) leaves a trail - but you can't invent clues to that trail until you know the details of what the trail is.

Yes that is sort of the purpose of this thread. I built up the informant situation without really thinking about who would get the information out and for what motive, and how to do it in a way that leaves some sort of trail for people to follow.

Jay R
2014-11-27, 11:32 AM
Yes that is sort of the purpose of this thread. I built up the informant situation without really thinking about who would get the information out and for what motive, and how to do it in a way that leaves some sort of trail for people to follow.

Oh - well then, let's stop talking about clues.

What do you know about Warlord A? Why does he want the city? Is it part of a war, and just in the way, or is there a treasure there he wants, or what? Is there time pressure? Does he need to take the city before the pring floods make it impossible, or before some other battle is fought? What would he be willing to pay for information to take the city?

How is the city ruled? Who's in charge, and who hates the ruler?

Is the person giving out information a traitor from the city, or a spy from the invading force?

Why isn't magic being used to get the info? Are there carrier pigeons? Why doesn't the warlord just send in his best information gatherers as a trading caravan?

Is there a specific person sending out information, or is the warlord just asking traders what they saw?

How many street kids have seen the messengers? How much information will they give for a coin or two?

And finally, do you want us to ask you for these details, or propose a scenario?

WarKitty
2014-11-27, 12:06 PM
Oh - well then, let's stop talking about clues.

What do you know about Warlord A? Why does he want the city? Is it part of a war, and just in the way, or is there a treasure there he wants, or what? Is there time pressure? Does he need to take the city before the pring floods make it impossible, or before some other battle is fought? What would he be willing to pay for information to take the city?

Ok think you're a bit off base here. Basically, big city A has a virtual monopoly on mining and quarrying and such. Their outposts are heavily defended to prevent other people from getting access to these resources, with both mundane and magical defenses. So you can presume the motive is basic resource control.


How is the city ruled? Who's in charge, and who hates the ruler?

Think some sort of merchant republic. There's a strong guild system and in practice the guilds control the city.


Is the person giving out information a traitor from the city, or a spy from the invading force?

Why isn't magic being used to get the info? Are there carrier pigeons? Why doesn't the warlord just send in his best information gatherers as a trading caravan?

Is there a specific person sending out information, or is the warlord just asking traders what they saw?

The city has an extremely strong, racially based, citizen/foreigner distinction. Citizens don't generally travel outside the borders, which are quite well policed. Foreigners are generally highly supervised, and this sort of information is heavily guarded. Think less "when does the watch change" and more "how do you make the key to command the golems" - you're not going to be able to just ask around, because common traders won't know anything of use.

You can presume protective magics are in place generally.


How many street kids have seen the messengers? How much information will they give for a coin or two?

The problem the way I'm envisioning it is less about finding out who saw who and more about figuring out what's relevant. You don't generally have such nuisances as street kids, though you have many children working in various capacities, especially among the servants. There's only one inn permitted to foreigners, so asking, say, the bell-boy, might produce results.


And finally, do you want us to ask you for these details, or propose a scenario?

Detail asking is good. I tend to have a very well developed idea of how a specific society works

As an added incentive, I'm thinking it might be fun to give the players a bit of a temptation to not turn the spy in while they're at it. They don't like the attacking warlord, but this particular city isn't that great either - bunch of racists hoarding useful materials for profit.

I'm thinking tentatively that a secretary could be a fun leak - it's the sort of society where no one pays much attention to the goings-on of servants. And everything is written down and filed somewhere. Tempt the appropriate clerk and you could have a lot of information on your hands. Of course, that's just the start.

Alberic Strein
2014-11-28, 09:22 AM
When you want an operative to go traitor, you need to get a hold of his vices.

1) Holding a family member hostage is the heaviest handed method and is really not subtle, doesn't really work for long term jobs

2) Addictions. People have addictions, whether they be sexual in nature or not, they tend to be pricy, illegal and secretive. Meaning you can have cold hard cash as the carrot, blackmailing as the stick, and the whole 'I can't talk about it' reaction to seal the deal.

3) Patriotism. It works. The society you describe looks close to Ancient Greece, people put an emphasis on the city. This can be used to blindside the local forces, who will look for an outsider, while the mole is actually a citizen who has the same cult as warlord A.

4) The thrill. Some lives can be pretty fraking boring. But being James Bond? Real spy talk? Being invited to a prestigious restaurant? THAT will get some people going.

So, you can create a few scenarios.

The Cult possibility: Warlord A belongs (for the sake of the argument) to the cult of The DEVOURER. Traitor A was raised by a devout member of that cult. Warlord A wanted inside information. So he sent his trusty Spy A subordinate disguised as a merchant to find a way to smuggle information in and out of the city. Spy A sniffed aound and found that Traitor A was a follower of the same cult as them. Spy A contacted Traitor A and was delighted to find that his ultimate loyalty was to The DEVOURER. So they had their inside informant. Now, how to get the information in and out. Why, with potteries of course. They trade items containing the information Warlord A needs. Since they use a commercial medium, Spy A and Traitor A don't need to be that much in touch, as long as the system works. Mission successful. Then, a ragtag bunch of misfits arrive and... Well, the next is up to your players.

Hooks:
-The medium, instead of potteries, could have a direct link with the cult they follow.
-The medium by which they trade messages could be busted, and while this doesn't out them, it forces them to organize a meeting.
-The cult could have some distinctive features, easily known about Warlord A, and the adventurers could hunt those who conform to such customs.

This also goes with your servant theme, Traitor A is a servant for Noble A and he uses the medium to leak info to Warlord A with the added protection that if anything happens, his master will be blamed, not him.

The Vice possibility: Traitor A is addicted to X. X could be a high class escort, drinking, illegal substances, etc... And he is short on cash. Warlord A, like before, needs a traitor, so he again sends Spy A to unearth one. Spy A discovers some leverage on Traitor A, who can get relevant information, either as a noble in power or as a servant of Noble A, and bribes him. They need some way to give him the money and get the information out of him. They can meet, or use another medium like before.

Hooks:
-This time there is a flow of money, so following it will lead to results. Traitor A spends more than he earns, which can be obvious to close scrutiny.
-Traitor A and Spy A will most likely need to meet. Which is dangerous.
-Addicts are unreliable, Traitor A might start asking for more, for too much, forget his place, forget to shut his trap and unwittingly provide leads to the adventurers.
-If they use a commercial medium to transfer the information, it holds the same flaws as precedently, however the money Traitor A earns will be legal, so the adventurers might stumble upon an utterly overpriced good which is actually the medium.

The I-Got-Your-Niece Possibility: Warlord A still needs info, Spy A is sent, but lo, while some people have the information needed, none have obvious reliable flaws. One, however, has a cute niece. One quick kidnapping later, they got the leverage needed.

Hooks:
-Traitor A will NOT cooperate happily with them in this scenario and may stealthily work to have the adventurers free his niece.
-Spy A will need to contact Traitor A with proof of them still having his niece, since there is no phone, they will have to meet in person (though not with the girl) which can lead to adventurers finding them.
-A kidnapping is not stealthy, not by a long shot, and even less in a closed off city, so it will raise a lot of attention. Hopefully the adventurers will pick up the intrigue.

There. Before going more in detail, which one has your attention?

Realms of Chaos
2014-11-28, 10:27 AM
While you effectively shot my ideas down involving actually going to the attack site, you didn't actually address the other main idea I brought up.


Namely, have the guilty party do something suspicious


Maybe one of the traders has a late shipment come in with stone from the quarry they shouldn't have access to.
Maybe the treacherous trader decided to perform some light looting before the town's destruction (since who would ever really know) and is currently trying to pawn off materials from that quarry that they shouldn't have had access to (Maybe they decided to rip some filigree free from the walls before they left, the ancient equivalent of ripping copper wiring out the walls).
Maybe the traitor(s) are so paranoid that they are continually seeking to shift blame onto others or are willing to straight-up kill anyone in their group (if person is not acting alone) that might possibly be having second thoughts.
Maybe the traitor is far too greedy and is already scouting the defenses of this city, just in case.
Maybe the traitor is notorious for having no luck in business but has just come into an unexplained windfall (or all of his or her merchandise has just jumped significantly in quality and price according to others).



Alternatively, knowing something about a trader may help if parties can actually talk to these individuals.

Maybe your party will catch a failed bluff check.
Maybe your party will learn that a trader would gladly sell his own mother for a copper piece.
Maybe your party will learn with an appraise check that the weaponry a trader carries was made by the raiders.
Maybe your party can learn that one or more traders have family, friends, or trade contacts among the enemy (if not directly, than through missives and other clues hidden amongst their wares or in their wagons).
Maybe the traitor expresses casual disgust for the attacked nation in all conversations or has been overheard decrying the current rulers in the tavern while drunk.



If you need help getting clues to players:

Traders under investigation may not make as much money. As such, any trader who has heard rumors about others has an incentive to deflect blame off of themselves so they can do business in peace.
A particularly nationalistic trader may volunteer any information he has about other traders without much prompting at all. The information gained won't be about the actual attack, of course, but will be circumstantial evidence and hearsay about the practices and values of other traders that can help with narrowing down suspects.


The simple fact is that if you want the party to know for certain who did it, the only clues you can really leave are past slip-ups on the part of the traitor. This may seem like a bit of a cop-out but keep in mind that most traders aren't professional spies and that the slip-ups need not be immediately obvious. If the traitor did his job perfectly, makes no mistakes, and there is nobody and nothing to provide direct evidence on what has happened, then the best your party can do is trying to set up a motive for a narrower band of suspects before approaching each one with more aggressive interrogation (hopefully making one of them flee or otherwise reveal themselves).