Well isn't this a nice little game, a creative idea executed fairly well.
The idea behind it is you're a private investigator in a violent town, trying to arrest an assassin. As a result, you investigate this filthy town while trying to stay alive.
The clues are randomly placed in the environment and you have to investigate every nook and cranny to get the clues that will reveal who the true culprit is. Some clues are more decisive than others, for example, a bullet casing may indicate the culprit is a Mobster or a member of the Police, while a Police ID precisely tells you the culprit affiliation.
You have to figure out 3 things : Affiliation (Civilian, Mobster, Policeman), Job (Driver, Chef, etc.) and Sex (Male or Female).
Of course you can just guess and try an arrest but if you get it wrong you fail.
As to how gather suspects, you have to talk to the people in various places, crime scenes don't have people lingering about but have generally more clues and some events make people amass in a place, particularly if they're from one affiliation.
Anyway, this becomes quite important when playing a higher difficulty than normal, because either the police or the mob want you dead, so the investigation becomes much harder with shootouts, especially since bullets are limited and costly, that's why it's wise to avoid places where the affiliation that wants you dead hangs out.
Bullets aren't the only thing that can kill you however, hunger can as well, you have to manage your money to buy the right resources like lockpicks, bullets or food to survive, everytime you investigate or talk with someone you get hungrier until you die.
Some places need lockpicks to explore fully and you can even rob some places where hopefully you don't get spotted or you make another faction your enemy.
Everytime you start a new game, the culprit and the clues are randomized, as is the faction that hunts you down, the events of course are randomized too, as is the place you can find clues.
The gameplay is free and you can go whenever you want mostly, but you have a time limit in days to catch the culprit... or you might just go on a murder spree.
All in all this is a repeatable noir detective story with a great soundtrack and a great feel to it. Recommended, but might get old pretty fast.