who did dillinger shoot and why?

I wasn't watching this movie closely but got more interested as it went along. It was sometimes hard to identify different members of the gang- at the last robbery, one guy gets shot and I think Dillinger goes back puts him over his shoulder and carries him to the car in gunfire. Later the injured guy is bloody and in bed, when the FBI comes I think Dillinger puts a pillow over his head an shoots him.

So what cast member was it that he shot and killed, and why did he do that? I know the cops were coming but it seemed unnecessary for him to blow him away- judging by his reaction when the bullets hit him he was still very much alive. Sorry if I got anything wrong it was hard to follow what was happening at the end.