Detectives were questioning a 22-year-old man today after a father 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's life on the pavement in west Croydon, south London on Thursday.
The pair were travelling to the nearby Mayday Hospital where her baby brother had been born hours earlier.
Detectives said the victim, aged 26, became involved in an argument with a second man, believed to be a former colleague, before the fatal blow was struck.
A 22-year-old man was arrested on suspicion of murder after handing himself in at a south London police station.
Police are hunting two teenagers wearing hooded tops who fled the scene and may have been involved in the scuffle.
A post mortem revealed the victim died of a single stab wound to the heart.
Security guards at a nearby office last night described how they took the little girl away.
One staff member said: "I said she shouldn't be watching something like that, I asked around to see whose child she was and somebody said she was the victim's, so I took her away into our building."
He said that the three-year-old was "in shock, her eyes were wide open". She was muttering under her breath occasional words like "mum" and "Mayday".
The employee said he watched paramedics working on the victim for a long time before the man died in front of his eyes.
He said: "Everybody else was in shock, she was so small, you didn't quite realise she was there. I just did what everybody else would do."
Emergency services were called to busy London Road, west Croydon, shortly after 6.15pm on Thursday night.
The victim, who was originally from Ghana, was taken to hospital where he was pronounced dead less than an hour later.
The short stretch of London Road is mainly specialist ethnic supermarkets, halal butchers and new-build flats.
A white forensic tent was erected over the bus stop and blue-suited forensics were examining the bus shelter and timetable for evidence.
Police found a number of knives in the area and were also reviewing CCTV footage from several cameras.
Det Ch Insp Cliff Lyons, who is leading the investigation, said the circumstances had left him and other officers extremely shocked.
He 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 said: "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, are working on the case.
Mr Lyons added: "This was a shocking attack in a public place in the early evening.
"The victim's three year-old daughter was with him when he was attacked, though fortunately she wasn't physically injured.
"Even more tragically, his partner had given birth to a son just that morning.
"The investigation is at a very early stage and I'm keeping an open mind about the circumstances of the attack at this point.
"A number of witnesses have already come forward but I believe there are still people with information we need to speak to and I urge those people to get in touch.
"In particular, we need to talk to two teenage boys who were at the bus stop when the incident happened who may have significant information.
"They are described as black, aged between 15 and 20 years old, of slim build and wearing hooded tops."
* Anyone with information should phone Crimestoppers on 0800 555 111.