A man was stabbed 24 times in a frenzied attack by a gang of youths in south London, police have said.
Det Ch Insp Dave Manning revealed the extent of Daniel Graham's injuries a week after the 45-second attack near East Dulwich railway station.
He said many young people who attended a party before the killing had failed to come forward with information.
Later officers will be patrolling streets, buses and trains in the area in the hope of speaking to witnesses.
Investigating officers provided new details of the attack as they appealed for help catching at least six men responsible for the 18-year-old's murder.
They have released CCTV images showing Mr Graham running towards the 176 bus and moments later as he got off the bus into the path of his attackers.
Mr Manning said: "This was a completely frenzied attack in full view of dozens of people.
"The attackers made no attempt to cover their faces.
"Witnesses described a gang raining blows on to him. Someone was hitting him with a bottle and others were kicking and punching him. Another man was described as punching him in the side."
Mr Graham was attacked after trouble flared at Dulwich Hamlet FC clubhouse and in the car park of an adjacent branch of Sainsbury's.
Police said between 50 and 100 young people from across south London attended an event at the club, falsely billed as a young woman's 18th birthday party.
Shortly before midnight shots were fired, leaving a 14-year-old with a gunshot wound to the leg.
As the panicked youngsters fled the building Mr Graham got on the bus in Dog Kennel Hill.
Mr Manning said: "Witnesses described him as clearly trying to avoid somebody and he was in a state of high anxiety and trying to conceal himself at the back of the bus."
Moments later he got off the bus and was attacked "in full view of dozens and dozens of people on the bus".
Passengers on the bus gave first aid to Mr Graham but he died later in hospital.
More than 40 police officers will be in the area handing out leaflets later and appeal messages will be sent to people in the vicinity with mobile phones using Bluetooth technology.
A 15-year-old boy arrested on suspicion of murder and a 13-year-old boy arrested over the shooting, both from Peckham, south London, have been released on bail.