With this background, you can roam the mansion watching people interact and looking for clues to see who you should choose. You can even talk to the characters as you try to make up your mind.
Postmortem doesn't get much more complicated than this in terms of gameplay. Instead, it forces you to make a difficult moral decision: to choose who dies. For this reason, your mission is usually to try to find out 'who deserves it most' or which consequences will be least disastrous.
Postmortem is a strange but original and unique game. The only issue is that it has a lot of text (in English) and is sometimes not as entertaining as it would like to be. Some characters are interesting, but others not so much.
This version of the game is free, but you can also buy a version with more features from the developer's site.