A man is being questioned by police investigating the murder of two sisters and their mother's boyfriend.
The three were found shot dead in the flat
Lorna, 34, and Connie Morrison, 27, and Noel Patterson, 62, were found shot at a flat on the Stonebridge Estate, in north-west London, last Friday.
The man, aged in his 20s, was arrested by armed officers in Tottenham, north London on Tuesday afternoon.
Police have been hunting three men seen near the flat. Lorna's nine-month-old son Christanio was not hurt.
The three bodies were found on Friday by a family friend.
'No evidence of torture'
Shots were heard the night before, but no-one reported it to the police.
Connie and Mr Patterson, a cleaner, had been tied up.
Post-mortem tests showed Mr Patterson had been shot three times in the head while Lorna was shot once in the head.
An examination of Connie's body is ongoing but police said there was no evidence of torture on any of the three.
Evelyn Daley, the mother of the sisters, had been at work throughout the night as a carer when the killings happened.
Police said they believed the family were specifically targeted but did not think they were involved in crime.