An 89-year-old woman has been stabbed to death at a home in Thornton Heath.
Ambulance crews called police to the home in Brigstock Road at around 9.20pm on Tuesday.
A woman was suffering stab injuries and was pronounced dead at the scene.
A man, aged in his 30s, was arrested at another address in Croydon a short time later.
He has been taken into police custody.
At this stage, police are not looking for anyone else in connection with the death.
The woman and the arrested man are believed to be have been known to each other.
Enquiries continue to establish the full circumstances.
The woman’s family have been informed, and they will be supported by specialist officers.
Formal identification and a post-mortem examination will be arranged in due course.
Anyone with information that may assist the investigation is asked to call 101, quoting reference 7790/21jun.
A spokesperson for the Metropolitan Police said: "An investigation has been launched following the death of a woman in Croydon.
"Police were called by London Ambulance Service at around 21:20hrs on Tuesday, 21 June, to a woman suffering stab injuries at a residential address in Brigstock Road, Thornton Heath.
"Officers attended along with ambulance colleagues.
"An 89-year-old woman was pronounced dead at the scene.
"The woman’s family have been informed, and they will be supported by specialist officers.
"Formal identification and a post-mortem examination will be arranged in due course.
"A man, aged in his 30s, was arrested at another address in Croydon a short time later.
"He has been taken into police custody.
"Enquiries continue to establish the full circumstances.
"At this stage, nobody else is sought in connection with the death.
"The woman and the arrested man are believed to be have been known to each other.
"Anyone with information that may assist the investigation is asked to call 101, ref 7790/21jun."
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