I don't think the police are there to intervene in petty squabbles like lunch theft, annoying as lunch theft may be. Getting the lunch owner fired, on the other hand, is a serious matter, and firing the thief and HR because of them doing this to the lunch owner is a proportionate response.
That’s exactly why they’re there. Would you say the same if the lunch was shoplifted from a business?
not going to help if HR was sleeping with the thief (which was later uncovered)