Hello Itsjo70 I have the feeling your grandson has been scared enough not to risk this again.
My son was 11 when he was caught the same way, although he was stealing from a school friend.
No prosecution but it took its toll and a lot of love and reassurance, talking though how he felt (angry and ignored because of recent family trauma) and my promise to always listen and be supportive.
Like your boy, he was normally polite and respectful, very loving and thoughtful and went on to make a career in the army. He now owns his own business.
I completely disagree that one should blame parents. It has been my experience that children also suffer in a combative and distressed household where parents "stay for the sake of the kids" and fight all the time.
Frankly, I see no point in blaming anyone - this is life, do your best to make a situation better, not worse by apportioning blame. How does that help?
Be optimistic Jo70 and just keep loving him unconditionally. 