Police are continuing to question a man after a 13-year-old schoolboy and his mother were stabbed to death in a "horrifying" attack at their home.
West Midlands Police said the suspect, in his 20s, was arrested after three victims, named locally as Tracey Wilkinson, her husband Peter and her son Pierce, were found stabbed in Stourbridge at about 8am on Thursday.
Ambulance crews attended but Mrs Wilkinson, who is understood to have been in her 50s, was pronounced dead at the scene.
Her son suffered critical injuries and was pronounced dead in hospital, while her husband remains in hospital with stab wounds to his chest and back.
Officers said a Land Rover stolen from outside the home on Greyhound Lane, Norton, was "intercepted" by police at around 8.30am in a nearby street, and a man thought to be known to the family was detained on suspicion of murder and wounding.
Dudley Police Superintendent Lee Kendrick said the killings were "horrific and heart-breaking" and the investigation was "progressing at pace".
He said: "Clearly our investigation is at a very early stage but we understand the suspect was known to the family and may have been living at the address - although he is not a family relative. We don't think this was a burglary or a robbery."
Detectives are trying to establish what the relationship was between the man and the family.
Mr Kendrick confirmed the suspect was known to police, but said it was "too early" to comment further.
No one else is being sought in connection with the killings.
Friends said Pierce was a pupil at Redhill School in Stourbridge.
The school said in a statement that pupils and staff would be given psychological support, adding: "Our thoughts and prayers are with those who have been affected by this."
A neighbour of the victims described seeing two people being carried from the house on stretchers into ambulances after the "horrifying" incident.
Asked to describe the family, the woman said: "We just knew them as neighbours and asked how the kids were when we saw them in the street.
"They were just really, really friendly, they had lived there about seven or eight years and what has happened is just desperately sad."
A woman whose property backs on to the Wilkinsons' house told reporters she heard a man shouting in a neighbouring garden at about 8am.
"It was definitely a man but I couldn't hear what was said. At the time I thought it was a workman," she said.
Numerous friends of the family, including several children, called at the victims' property to place floral tributes beside the police cordon.
One bunch of flowers, left by a teenage boy, had a card which read: "RIP Pierce, you will never be forgotten. We had so many good memories and I hope you are safe up there, fly high bro."
Another card said: "The most amazing family! So many memories that we will always treasure. Gone but never forgotten."
Two police officers have been discharged from hospital after suffering minor injuries when their vehicle was rammed before the Land Rover crashed into a garden wall, West Midlands Police said.