A guy who is ripping off backpacks from unlocked cars isn't in the mafia or the Yakuza: He doesn't have a group of thugs to call upon. And I doubt he takes it terribly personally -- rip people off and you'll get burned eventually. Acting hurt and vindictive about it seems pretty foolish.
I'm extremely surprised that the police paid any attention to this: Keeping valuables -- well, not really valuables -- in an unlocked car...that just doesn't fit the bill of the sort of crime that the police will even show up to your place for a statement. That the officer(s) actually put in legwork, and the justice system carried out a sentence, makes it almost hard to believe.