[Sly]

One of friends works at a small corner store and caught a guy around 19 or 20 years old stealing adult mags and some pop, without the guy noticing my friend walks behind him and puts him in a lock head and punches him in the face relentlessly till he dropped the goods. My friend then let him go and told him if he ever comes here again, he'll kill him (obviously over the edge). Seeing that this store he works for is his parents business, I can understand why he would go to such extremes to deal with thieves, at the same time I'm afraid the guy might come back with the police and press charges for assault. My friend said he was 'allowed' to attack the guy since he was technically 'stealing' under his parents property. In addition, I asked him why didn't he call the police before attacking the guy. He told me apparently there were a lot more thieves before and that the police could not track them since so many of them came in bunches. Anyways, does my friend have a case here? Or is he just putting himself into trouble?