Caught red-handed !
The volunteer and I went down today. This woman complained that there were a lot of cats around the void deck of her sister-in-law's flat. We didn't see more than four cats between the two void decks, but I did see one cat run upstairs, and when we followed them up, there were these three cats in the corridor. We spoke to the man whose flat the cats ran into and asked him to please try and keep them in.
He also mentioned another woman fed some cats in the void deck - the ones we saw were all sterilised except for one cat.