bcc1357: Well, the survivor should be judged for three murders, not the gunman.
In some jurisdictions there is such a doctrine. When committing a deliberate crime, the responsibility for all the bodies that appeared as a result of the crime lies with those who committed the crime and not with those who made the bodies.

If it is group, then all members of the group are responsible. Or those who survived. They are also responsible for the bodies of their partners.

For example, even if a police officer shot one of the members of the group, the rest of the members are charged with killing that member. The victim defended. Then the other members sit.

And then it is very easy to solve the question of what "no one has to answer, so we lay down the one who defended".

Or if someone enters your house in the process of committing a crime, and you are the one of him, then he himself is considered to be guilty of killing him. And if at this time in the car was sitting his partner, then the guilty in his murder is considered his partner.

Very good doctrine. We could take them, but they don’t care who they are. The important thing is that someone sits down so that it can be completed. If so, let those who commit crimes be put to death, not those who are forced to defend themselves.