I at first thought it to be the handiwork of a Muslim couple (a pivately held suspicion), but I stand corrected, the deed was committed by other totalitarians, of the Leftist garden-type variety.
Alleged captors ran notorious Communist collective in London before taking women as slaves: police

The balcony on the first floor appears to have been used for storage; an unkempt hedge screens the ground floor windows, preventing those living on either side from seeing who went in and out. Members of the local community say the estate is a friendly place to live.
Many of the blocks overlook each other, and people say they know everybody by face if not by name. But the residents of this particular house — a couple of Indian and Tanzanian origin, both aged 67, and three women aged 69, 57 and 30 — stood out because they were so reclusive.
They were the dominant ones, you could tell that
“I thought the elderly couple were looking after the others, as if they were carers,” said a resident who did not want to be named. “But there was something strange about it all. The older couple were definitely the ones in charge. They were the dominant ones, you could tell that.”