Well, it is definitely evidence of smoking marijuana. The problem is whether it is 12 or five or 20, it affects people differently and a lot of it has to do with how, what do you call it, how used to it, how often a person has taken it before. If you take it more often, it has less of an unpredictable affect.
It could have been a factor in his behavior, but the best measure of his behavior is what he was doing all day. Was he acting different than he usually did, for example, and that would be for friends and relatives or witnesses who saw him during the day. Was shoplifting cigars a great departure from his usual behavior.
So great of a departure that one could say he was influenced by the marijuana or did he do that sometimes when he didn't have marijuana.
It is interesting that no other drugs were found and no other medications were found. I couldn't find if he had been taking any other medications that he had stopped taking.