The traditional game of Assassin, with a few small changes.
It becomes a way to make money.
Each person starts with 20$US, maybe more or less if you want. Each player is required to keep their money with them at all times.
When a player is assassinated, the assassin can 'loot' the 'body' and
take that person's 20$US - and they must then keep that money with them at all times, too. If they get assassinated, their killer gets the original 20$US + all loot.
At any time, a player may 'retire' and keep his/her money, but they lose the chance to get more.