@Coreen,
Every son is a good boy, Coreen, until he's not. Kids are also apt to stretch the truth to make their misdeeds seem less their fault. Determine, first, if he's telling the truth about being bullied into doing what he did.
If he was only held for a few minutes for shoplifting, which is a pretty serious deal, especially these days - companies seem to take a much harder line stance on it than when I was young, then it seems like he's had a golden reprieve.
Talk to him, a lot, showing your concern for him as your son, but don't let him forget that what he did was wrong, and that court systems rarely buy into the "they made me do it" excuse.