An elderly woman was stabbed to death at a home in Croydon.
The 89-year-old victim was found suffering stab injuries at the home in Brigstock Road, Thornton Heath at around 9.20pm on Tuesday.
Paramedics pronounced the pensioner dead at the scene and called police.
A man known to the victim was arrested on suspicion of her murder nearby.
The woman’s family have been informed, and they will be supported by specialist officers, police said.
Police said a post-mortem examination will be arranged in due course.
A man, aged in his 30s, was arrested at a different house in Croydon a short time later and remains in police custody.
A Met spokesman said: “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 have been known to each other.”
Anyone with information that may assist the investigation is asked to call 101, ref 7790/21jun.