A 62-year-old man and two sisters have been found shot dead at a flat on a north-west London estate.
Neighbours reported hearing gun shots on Thursday night
A nine-month-old baby, also found at the Stonebridge Park flat in Wembley, was uninjured but covered in blood. The boy has been taken to hospital.
A family member discovered their bodies and called police on Friday afternoon.
Police said the deaths of the women, aged 27 and 34, who were related to the baby and the man, thought to be their father, are being treated as murder.
Armed officers were called to the scene and high visibility patrols have been taking place in the area around the flat in Clark Court, Stilton Crescent.
The Met said officers were called just before 1500 BST. Neighbours reported hearing gun shots on Thursday evening.
Fal Patel, 28, who lives opposite the eight storey block of flats where the murder took place, said she initially thought the police activity was related to a security alert.
"But officers told me there had been a serious incident at the flat and I realised it must be murder," she said.
Another neighbour, Nilesh Mansuklal, 36, described the male victim as a popular man.
"He took the time to talk to people and always seemed to have a smile on his face," he said.
"It makes no sense that somebody would want to take his life. He didn't look like the type of person to ever get into trouble."
Police said they are keeping an open mind as to a motive for the killings.
The victims were found in the same room and were pronounced dead in the flat.
Ms Patel said she was surprised to see so many officers at the scene.
"The police often circle this estate. It's notorious for drugs and crime but even here seeing this number of police teams is rare," she said.
A post-mortem examination of the victims bodies is expected to take place on Saturday.
Police are informing their next of kin and the baby has been put in the care of social services.
Operation Trident, an initiative to tackle gun crime among black communities, is investigating the deaths.
No arrests have been made so far.