Four Boys and a Gun

Four boys are involved in a robbery in which a policeman is killed. Caught, they are told they will most-definitely be convicted. Three will get life sentences and only one will be given the chair if they tell who pulled the trigger. Left to themselves, the boys must decide which will forfeit their life for the others. Will it be the one who actually pulled the trigger, the one who has a family, the one who brought the gun in the first place, or the one who has the least prospects of leading a happy life if ever paroled.