Investigation

[VerastheBrujah]

I'm running a campaign in which the PCs recently helped a ghost exact vengeance on the man who murdered him nearly 50 years before. The man was a citizen of a very powerful nation, which spares no expense in avenging the death of its citizens. Naturally, an investigation will ensue, and early indications point to either foreigners or elves (which are viewed much like goblins are in this world). This means that the investigator will have access to almost any magic that he needs to track down the strangers who were involved. Even though he would likely be able to conclude that it was a ghost, he is convinced that the strangers had something to do with it, as this happened in a rural area in which very few people pass through. The fact that a handful of strangers showed up immediately before the killing and disappeared without a trace immediately after cannot be coincidence.

Unfortunately, I am weak on my knowledge of magic, and I'm not sure what spells could be useful. Having looked through the PHB, I found nothing that will help him, as he does not have an object once owned by any of the PCs (one of them did spend a few silver pieces in the tavern where the killing happened, but there would be no way to distinguish them from the other coins).

Did I overlook anything that might be useful? The next story arc will be either 1) them trying to escape being hunted down or 2) them dealing with the fact that a nearby elf tribe that they have befriended is being blamed for the killing, which is what will happen if the investigator hits a dead end.

Here are more details from the investigation before he would request spells, if it helps. They are written from the investigator's perspective.
-8 witnesses to the killing, each with a different story. Combining the stories, this is what happened: 5 or 6 people entered the tavern. One ordered a drink and had a heavy accent (from the smaller, weaker nations to the south). Some or all were elves, and one seemed to be a priest (from a very organized, hierarchical religion unpopular in this country, but strong in the southern nations).

-Shortly after they entered, a spirit manifested, and argued with the victim. There was some mention of betrayal. The victim called the spirit, "Orlando"

-Spoke to the victim's sister: an elf, a priest, and a man in rags (all with thick accents) came to her home earlier that day. The man in rags mentioned Orlando's name upon seeing her son, saying that he needed to "take responsibility."

-Orlando was a mercenary alongside her brother who was killed in battle nearly 50 years earlier.

-He would get one of Orlando's old possessions, but he moved on after the killing, so he would obviously be impossible to locate. If you need any more, please just ask.

[Mnemnosyne]

How powerful an ability are you looking to use for this? And how many resources?

Contact other plane or commune can probably get a solid lead on which way they went, or which way they're headed, with the right questions. Scrying will get you their location to some degree. Other people have seen them and can thus provide a description; they get a will save with a +5 bonus, but you can reduce that to +3 by making a portrait of them based on descriptions from the witnesses. Get some sketch artists in there, make a few portraits, show them around to figure out which one is the closest likeness. Pick on the one most likely to have a low will save (anybody look like a fighter-type? Yeah, that's probably a good target to scry on.) and if you're willing to cast it over and over, well...they're going to fail their save eventually.

After you've seen them through scrying, you can probably get some idea as to where they are, which you can then confirm through commune or contact other plane. If they're important enough to pull out the really big guns on, there's always metafaculty.

[VerastheBrujah]

The party is all 4th level, so I was planning on keeping the Justiciar who is hunting them at mid level. That being said, he has the authority to go to the wizard organization or a church and get spellcasting services. Let's say that he has a budget of 1500 gp for the investigation.

Metafaculty is out on principle--Psionics has no place in this world. Commune would be too expensive, thanks to the 100 XP cost. Scrying and Contact Other Plane would probably work best. He is unlikely to be able to find them with these spells, but they will probably lead him to the elven tribe.

If I go this way, it looks like the players are going to have to deal with the fact that they started a war that will inevitably result in the complete elimination of this tribe.

Thanks for the help.