A 13-year-old schoolboy and his mother have died after beingstabbed in a "horrifying" attack at their home.
Tracey Wilkinson, her husband Peter and her son Pierce, were found stabbed in Stourbridge at about 8am on Thursday.
A man in his 20s, who police have said is known to the family and may have been living at their address, is being questioned over the killings.
He is not a relative and detectives have ruled out robbery and burglary as a motive.
A local woman who knew the family indicated they had taken a man into their home, described in some reports as homeless, at around Christmas-time.
Ambulance crews attended but could not save Mrs Wilkinson, who is understood to be aged in her 50s, and she was pronounced dead at the scene.
Her son suffered critical stab injuries and was later 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: "What has unfolded here this morning is horrific and heart-breaking. Police and ambulance were confronted with an awful scene: a man, woman and boy all with very serious stab injuries
"The woman and boy were found in the house and the man in the garden.
"Tragically there was nothing that could be done to save the woman - and her son later died in hospital from his injuries. Our hearts go out to the victims' family and friends at this devastating news.
"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.
"Our investigation is progressing at pace and we are working to understand exactly what the relationship was between the man and the family. At this stage we are not looking for anyone else in connection with the incident."
Friends said Pierce was a pupil at Redhill School in Stourbridge.
The school said in a statement to parents and pupils: "You may be aware that there was a serious incident in the Stourbridge area this morning which has affected our school community.
"Tragically one of our Year 8 pupils and his mother have died.
"Pupils and staff who need support will have access to psychological first aid provided by Dudley educational psychology service. We will also be providing parents with guidance on how to support their children.
"Our thoughts and prayers are with those who have been affected by this."
Meanwhile, Mr Kendrick confirmed the suspect was known to the police, but said it was "too early" to comment further.
He said: "He is known to the police.
"At this moment in time, it's too early to look at and release the details as to any previous dealings he has had with West Midlands Police, however he is known to the organisation."
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 added: "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 added.
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