Police in Brixton said the man they have arrested following a fatal stabbing where a 28-year-old woman was killed trying to protect her younger sister, is known to them, but would not give any more details.
Speaking this afternoon, Detective Reynolds said young children were at the scene of both attacks, which involved "extreme violence", and officers are trying to establish whether they saw anything significant.
More top news
Former BBC Apprentice contestant Stuart Baggs has died, a spokesman for his firm has said.
Tonight: a woman awaiting a double hand transplant, a dream realised through strangers, and a family who quit their life to travel Britain.
In the three years since Liam Lyburd was expelled from Newcastle College he built up an anger and resentment for the college.