Wow, quick round. Nice, I voted for the killer! Reserve me for next round please.
*EDIT* and I have some ideas for the spy
1. the spy has 2 guesses of who the killer is and then is allowed to choose one person to execute.
2.Once the 2 guesses are up the killer can kill the spy, he can be executed at any time.
OR
1. the killer can be killed and executed.
2.he has 3 guesses and if he got it right can tell everyone who the killer is, they have a choice to vote.
Or
1. the killer can be killed and executed
2. if he knows who it is he can then tell everyone hints to who he may be, for example "he is in the top half of the player list"