A man stabbed his former partner to death outside a nursery minutes before he was hit by a high-speed train on tracks in west London.
The 32-year-old woman was attacked in her car, near the Old Actonian Sports Ground in Ealing on Thursday afternoon, while her son sat on the back seat.
A man, believed to be her former partner, died 20 minutes later on the tracks at Hanwell station.
Police are not looking for anyone else in connection with the deaths.
A Metropolitan police spokesman said: "We believe we know the identity of both parties and next of kin have been informed but at this time no formal identification has taken place.
"We can confirm we are linking the two incidents, which we believe are domestic-related. The police are not searching for anyone else at this time in connection with this enquiry."
Police were called to Gunnersbury Drive, Chiswick, at 1649 BST on Thursday where the woman had been seen being stabbed. She died less than an hour later at New Ealing Hospital.
At 1711 BST police were informed about the railway death.
Train services were seriously disrupted in and out of London's Paddington station, after the man was hit by a train arriving from Bristol Temple Meads.
The Caterpillar Day Nursery, situated in the sports club grounds, was closed on Friday while the police investigation continued.
A group of people arrived to leave flowers at the scene of the stabbing.
Residents said the street was normally quiet.
Mary Davenport, 60, said: "It is unbelievable. Nothing really serious happens around here so it's a bit scary. It is quite frightening."
Police will be speaking to people who saw the stabbing - thought to include other mothers picking up their children from the nursery - and commuters who saw the man jump onto the tracks.
The results of post-mortem examinations being carried out are yet to be released.