You can prevent three people from dying if you kill one yourself. This would be the morally correct choice to make

If you don't do it, it's not really your fault, nobody has to know about the deal, and if you kill someone its on you and they will probably ignore the 3 people and arrest you for the 1 because our court system is flawed in such a way that allows this to happen.

Fallacy Of Red Herring

Legal repercussions don't have bearing on the morality of your action

You can prevent three people from dying if you kill one yourself. This would be the morally correct choice to make

What if it were 3 Hitlers that you could save?

Fallacy Of Red Herring

This is a more fundamental argument and assumes we know nothing about the person