Police are calling on people to abandon “misguided loyalty” and come forward with information about the murder of Hampton teenager Jamil Palmer.
Mr Palmer, 18, of Belgrade Road, Hampton, died of a stab wound after being taken to a hospital in central London.
He was stabbed close to Crane Park in Evans Grove, Feltham, shortly before 3.30pm on Tuesday, May 6.
Detective Chief Inspector Noel McHugh, of the homicide and major crime command, issued a fresh appeal for witnesses.
He said: “Jamil was attacked in Crane Park shortly before 3.30pm and the park would have been busy with people.
“Some witnesses have come forward to assist us with our investigation but I am certain there are a number of other people who have yet to speak to us.
“It is clear that there is a misguided loyalty where some people are not speaking to the police, protecting those involved.
“I would ask those who are reluctant to come forward to do so, so Jamil and his family can get the justice they deserve.
“I would also like to reiterate my reassurance to anyone who has witnessed this horrific attack that my officers are here to protect you and will treat any information you have with the utmost sensitivity and discretion.
“The park is popular with dog walkers and other park users - if you were in the area between 3pm and just after 3.30pm and witnessed this incident, or the events leading up to or immediately after the incident, you may hold vital information.”
Prior to the stabbing, Jamil had been at a friend’s house at the nearby Butts Farm Estate and he left the property at about 3.15pm.
The former Hampton Junior School, Teddington School, Richmond College and Kingston College student’s mother pleaded for people to reject “street code” and come forward with information.
Ashifa Sayani said: “Do the right thing in Jamil’s memory. Forget your street code, it is not grassing and it is not cool.
“Just tell the police what happened and who was involved.
“I’ve lost my son. The hurt that has been caused is unimaginable.”
An 18-year-old man and a 16-year-old boy were arrested on suspicion of murder on the same day.
They have both since been bailed and are due to return to police in early June.
After the attack, the attackers fled toward the A316 Chertsey Road.
Anyone with information should call the incident room on 020 8785 8099 or call Crimestoppers anonymously on 0800 555 111.