A man has been stabbed to death at a vigil in memory of another recent knife attack victim.
Police were called after a fight broke out between three men at the memorial event in Croydon, south London.
One of the men was stabbed - and pronounced dead at the scene.
Detectives say he was 23-year-old Reece Young, whose family is now being supported by specialist officers.
The other two men fled in a vehicle before police arrived, but later turned up at a south London hospital with stab wounds, believed to have been sustained in the fight.
The Met said some of its officers went to the hospital and arrested both men on suspicion of murder.
The first, aged 33, remains in hospital where he is being treated for non-life threatening injuries.
After his arrest, the second man, believed to be in his 30s, allegedly assaulted police officers and NHS staff before forcing his way out of the hospital.
Police are now trying to trace him.
Detective Chief Inspector Richard Vandenbergh, who is leading the investigation, said: "We believe this incident was witnessed by a number of people.
"They had gathered for a small vigil in remembrance of another recent fatal stabbing victim when an altercation began.
"Some of those people have already spoken to police, but I believe there are others who captured images and video of what happened.
"I need those people to contact us immediately.
"The information they have could prove vital in establishing the chain of events that has led to a young man losing his life.
"One arrest has been made and my team are working with colleagues across the Met to establish the whereabouts of the second man.
"We believe he suffered injuries that require urgent medical attention. He is urged to make contact with us immediately."
Anyone with information is asked to call police on 101 or tweet @MetCC quoting CAD 7449/30MAR.