Two 16-year-old boys have been arrested on suspicion of murder over the death of a 17-year-old.
Ezekiel Clarke died shortly after he was attacked in Churchfield Lane, near Castle Retail Park in Nottingham at about 19:00 GMT on 19 February.
Police said a 19-year-old man arrested on Thursday on suspicion of murder had been released on bail.
Officers are also looking to speak to the occupants of a white van and red car seen in the area at the time.
Det Insp Rich Monk of Nottinghamshire Police said: "We believe the drivers of these two vehicles could have vital information about what happened and we are really keen to trace them."
An 18 year-old man arrested on Friday on suspicion of murder has since been released.