A man was stabbed to death as he travelled with his three-year-old daughter to hospital where his wife had given birth hours earlier.
The little girl was left standing in horror as paramedics desperately tried to save her father on the pavement in west Croydon, south London, on Thursday evening.
The pair were travelling to the nearby Mayday Hospital, where her baby brother had been born.
Detectives said the 26-year-old Ghana-born victim became involved in an argument with a second man, believed to be a former colleague, before the fatal blow was struck.
Last night, a post-mortem examination revealed that the victim died of a single stab wound to the heart.
Police are hunting two teenagers wearing hooded tops who fled the scene and may have been involved in the scuffle.
Security guards at a nearby office described how they took the little girl away from the scene.
One staff member said the child appeared to be in shock. "Her eyes were wide open and she was muttering under her breath occasional words like 'Mum' and 'Mayday'."
Emergency services were called to London Road, west Croydon, shortly after 6:15pm.
The victim was taken to hospital, where he was pronounced dead less than an hour later.
Detective Chief Inspector Cliff Lyons, who is leading the investigation, said the tragedy "must prick people's consciences and encourage them to come forward with any information they have".
Mr Lyons said he could not rule out a random attack. He added: "It is a double tragedy for the three-year-old, his wife and the son he will never see."
The detective said between 80 and 100 police staff, including 50 detectives, were working on the case.
A 22-year-old man was later arrested on suspicion of murder after handing himself in at a south London police station.