I went to another mediation after the one with the black and white cat. The complaint was similar - that someone was feeding the cat upstairs and they were defecating around.
I managed to speak with the feeder and she insisted it was the 'corridor' cat but no one else on the corridor seemed to be very happy with it. The feeder claimed the woman opposite was feeding, but the woman opposite said the cat was defecating. Another man I spoke with said that the feeder had not sterilised and the cats had given birth several times. Yet another complainant said that the woman liked to wash the defecation down the staircase and it was outside her house. Another person told me they had adopted a kitten from her and they kept their cat inside now all the time.
What was interesting was that NONE of the neighbours asked that the cats be taken away. When I explained sterilisation, they were receptive. One had never complained because she didn't want the cat taken away. Another didn't know they would be taken away - she kept insisting they were lives and should not be taken away, but she did not know whom to turn to. She had spoken directly to the feeder and the feeder had scolded her.
I told the feeder that she had to feed them downstairs, and to get them sterilised, but she insisted they were not 'her' cats so why should she? I left her all the information and told her how much it cost and she said she'd think about it. She also said she might stop feeding - which is what so many people say when you ask them to please just feed downstairs. Apparently either the HDB or TC has also paid this woman a visit in the past.