Two women have died and a man and a teenage boy suffered serious injuries after reports of a stabbing in Milton Keynes on Christmas Day.
A 49-year-old man from Milton Keynes, Buckinghamshire, was arrested on suspicion of murder and attempted murder and is in custody, Thames Valley Police said.
Officers were called to a block of apartments in Santa Cruz Avenue, Bletchley, at about 6.30pm on Wednesday.
The women, aged 38 and 24, died at the scene.
A man, in his late 20s, and teenage boy were taken to hospital with serious injuries. They are both in a stable condition, police said.
A dog also injured in the incident was taken to a vet but did not survive.
Senior investigating officer Detective Chief Inspector Stuart Brangwin, of the Major Crime Unit, said: “Firstly I would like to extend my deepest condolences to the families of the women who have tragically died in this shocking incident.
“We have launched a double murder investigation which may be concerning to the wider public, however we have made an arrest and are not looking for anyone else in connection with this incident and the parties are known to each other.
“Members of the public will see a large police presence in the area while our investigation takes place.
“If you have any questions or concerns, please feel free to approach our officers and they will do their best to help.”
Anyone with information or footage is asked to call 101, quoting reference number 43240622935, or contact Crimestoppers on 0800 555111.