The family of a student who was seen "jogging along" after being fatally stabbed has urged witnesses to help bring his "cowardly" killers to justice.
Lewis Elwin, 20, died in Tooting, south London one week ago after he was knifed in the back in a road busy with parents on the school run.
On Monday his family appealed for help to stop "the epidemic of murders plaguing our young men" as murder squad detectives returned to the scene to encourage witnesses to come forward.
A reward of £10,000 is available for information leading to the arrest and conviction of the killers.
Mr Elwin's family said in a statement: "We need your help. We are appealing for any information that could help find and bring the cowardly killer or killers to justice.
"Words can't describe the pain and loss we feel. We are still in shock. We pray that this doesn't happen to your son, your brother, your family.
"But if our community continues to stay silent then Lewis's senseless murder would have been for nothing. Now is the time to come together and unite in our fight against knife crime; and the epidemic of murders plaguing our young men."
Scotland Yard said he was dropped off in Moyser Road, at the junction with Ribblesdale Road. He called a friend at 3.36pm arranging to meet them, and four minutes later was seen jogging along Penwortham Road, before he collapsed in Thrale Road.
Detective Chief Inspector Diane Tudway said: "I am of the belief that Lewis had already been stabbed when he was seen jogging along Penwortham Road.
"I continue to retain an open mind as to the motive behind the murder. There are a number of lines of inquiry ongoing to establish the circumstances of the incident and I am very keen to understand what took place between 3.36pm and 3.40pm.
"We have spoken to a number of local people but have limited information about the events of that day. I am appealing to anyone who is yet to come forward to do so with the confidence that they will be treated with the utmost sensitivity."
Mr Elwin was attacked near the home of London mayoral candidate Sadiq Khan, who called the murder "very worrying and troubling".
Ms Tudway added: "It is important that we build as clear a picture as we can, so that we can establish who attacked Lewis and what the motive may have been. We also need to find the murder weapon and identify where the attacker went immediately after the incident.
"I am aware there has been speculation within the community as to the motive behind the murder, and this is understandable. But we need witnesses to tell us what they themselves know about what happened to Lewis.
"Moyser Road is a busy residential road and runs between Mitcham Lane and Furzedown Drive, and I am confident more people would have seen or heard something."
When he died Mr Elwin was wearing a black jacket with a fur-lined hood, blue jeans and black Nike trainers with silver spots. He was carrying a black bag with a Nike logo and a long shoulder strap.
His family said catching the killers would allow him to "truly rest in peace".
"Someone knows what happened to Lewis," they said. "Please contact Crimestoppers anonymously. Any information is vital, no matter how big or small to the investigation. Your name, contact details or any other personal information will not be taken or disclosed. But the information provided could lead us to Lewis's killer or killers and help him to truly rest in peace."
Anyone with information can call police on 020 8721 4005 or Crimestoppers anonymously on 0800 555 111.