Slander
Explorer
There are a lot of aspects to consider. I don't think anything like Geneva rules should have any bearing on this decision except in the most progressive (read modern) of societies. Prisoners of war in the middle ages were not treated exceptionally well, and death was all but assured if they rebelled.
The bottom line is the lizard man was living on borrowed time. PCs were not obligated to let the lizardman live. He would have been killed right away except the party had use for him. There was an agreement that as long as the lizardman proved useful, he would live. Alerting guards isn't useful to the party by any stretch of the imagination, even if it was expected.
Now, if the lizardman lived up to his part of the bargain, and THEN he was slain, there would be more justification for a confrontation with the warlock. But as it stands, the worst thing the warlock did was deprive the party of an asset. If you want to confront him, confront him on that, not "killing a prisoner".
The bottom line is the lizard man was living on borrowed time. PCs were not obligated to let the lizardman live. He would have been killed right away except the party had use for him. There was an agreement that as long as the lizardman proved useful, he would live. Alerting guards isn't useful to the party by any stretch of the imagination, even if it was expected.
Now, if the lizardman lived up to his part of the bargain, and THEN he was slain, there would be more justification for a confrontation with the warlock. But as it stands, the worst thing the warlock did was deprive the party of an asset. If you want to confront him, confront him on that, not "killing a prisoner".