It was a similar situation here - our former neighbor apparently had NO IDEA the tenants he'd originally rented to had moved and illegally sub-let the place to their music-blasting, pot-smoking, non-dog-mess-picker-upper college kids. He didn't have a professional property management firm and whenever he planned routine inspections the parents came back and pretended to still be living there. We didn't know he didn't know, and along with many other neighbors were totally fed up with the situation. It was actually the condo board that got in touch with him (we personally didn't have his contact info or we certainly would have used it). He turned things around as immediately as possible once he'd been fully informed.
a friend HAD a professional company, but they weren't doing as contracted so the friend had no idea her house had become a drug den until she saw the news one night and there was a piece on a house that was raided-HERS. the entire garage and several rooms had been converted into a grow house while the rest of the place was party central. tens of thousands in damages but fortunately for her the management company was liable. she was upset w/the management company but surprised none of the neighbors had ever contacted her to let her know (her childhood home-inherited and she lived close enough that if she had gotten word on what was going on she would have taken steps to put it to an end-incarceration for the renters took care of that).