How about an email telling owners that, because of unsavoury incidents and illegal behaviour in the past, the committee has discretely installed security cameras in common areas. They have been positioned so that they are not immediately obvious, to avoid intereference, but you can see them if you look hard in the right areas.
Then once the nasty neighbours have gone send another email saying “Sorry, we meant we were thinking of installing security cameras.”
Or find out where they are moving to and send them a letter from the committee wishing them all the very best at their new address.
Or install something like these cheap surveillance cameras