So there are questions about what if any trial process they went through and then questions about fair and just punishment probably not including being sacrificed to an ancient evil weapon considered to heinous it was locked beneath the ocean behind dozens of counter measures alongside dozens of other artifacts of great power. Like, I believe that Deus is honestly trying to consider the global fate of all humanity on Earth and has decent intentions even if he may be motivated purely by greed and a desire to maintain a personal standard of living with everyone else being happy and healthy as a means to an end.
Initially. I personally think its pretty clear by now the bit about Greed was just a smokescreen.
By all account Deus already has the degree of wealth where he could not use all of his money if he actively tried. I mean. This guy decided having a personal island wasnt &%¤ enough, and went ahead and got himself a personal country.

While as for trial. Well the purpose of those is to establish guilt, and protect the innocent.
These were seemingly armed mercenaries caught planning terrorist action. People are executed for less than bombing hospitals.
And lets not get into the actual morality of this. But i hope everyone agrees that -if- anyone deserves execution, its scum like this.

By all account Deus does care a lot about guilt versus innocence, when he even discipline his personal right hand.

While as for the weapon. Nothing we have been told indicate its evil itself.
It just encourage mass murder because its to useful.

It's implied he only has her kill mercenaries.
More than implied. Straight up stated its only mercenaries illegally entering the country on a mission that gets a visit from Vale.