How to place players in team based on how many player's they've killed

I'm trying to make two teams that are the "good guys" and the "bad guys". I'd like it to be like a reputation system where you get good karma for killing bad guys and bad karma for killing anyone but the bad guys.

So far I'm using the following commands:

/scoreboard teams add Team1 Fugitives

/scoreboard teams option Team1 color red

and

/scoreboard teams add Team2 Rescuers

/scoreboard teams option Team2 color blue

I'd like use a command or a command within a command block to do something like the following.

if(playerkillsplayer = true){
variable + 1
}

if(playerkillsFugitive = true){
variable - 1
}

if(variable > 0 ){
team ==  Team1
}

if(variable < 1){
team == Team2
}

How can I do this?