Two people are being questioned over the murder of a teenager who was stabbed in Liverpool.
Aaron Morris, 18, was found in Wycliffe Road in Anfield on Tuesday night. He was taken to hospital with serious injuries but died on Friday morning.
A 16-year-old youth from Kensington and a 20-year-old man from Anfield have been arrested over his death.
Police are appealing to a man who telephoned them about the incident to call them back.
Det Ch Insp Chris Green said: "Over the last few days a man has called the incident room and spoken very briefly with officers about the incident.
"The man would not leave his contact details. I would appeal for this man to call back as his help with the investigation may be invaluable.
"I would plead for anyone with any information, even those who ordinarily may find it difficult to have contact with police, to come forward to help us get justice for Aaron and his loving family.
"Any detail, no matter how small and insignificant it may seem, could help in this investigation and can be treated confidentially.
"Our priority in this matter is to bring those responsible to justice."
A 16-year-old youth from Kensington and an 18-year-old man from Anfield previously arrested on suspicion of assault have been released on bail.