Lynching Victim's Odd Morality

I listened to an archived interview with the founder of the "Black Holocaust Museum" James Cameroon. 1930 he was almost lynched in the Marion, Indiana, his friends were, (see above). Cameroon recounts the entire episode from hanging with his friends to nearly hanging with friends in a more deadly way. The odd part of the story for me, that wasn't picked up on by the interviewer, was at the point of the armed robbery that got him arrested.

Cameroon and his friends hang out. They decide that they need beer money, I understand. Cameroon and his friends come upon a couple in an isolated car in lover's lane. One of Cameroon's friends hands him a gun. Then Cameroon notices that the man is one of his shoeshine customers. The man is the car is nice guy. Cameroon tells his "friends" he can't rob one of friends and hands over the gun and leaves. It turns out later that of the couple in the car come to bad end, the man is killed and woman raped.

What I don't understand is if James Cameroon was unwilling to rob someone he knew why was willing to standby and let someone else do the "job". At the point when Cameroon decided, as he says, that he wanted no involvement in an armed robbery he was holding a gun.