Police have named a 17-year-old boy who was stabbed to death in Cambridge as Jesse Nwokejiobi.
Officers were called to the scene near Logan's Meadow, a small reserve next to the River Cam, by the ambulance service at 2.52pm on Saturday.
Jesse was pronounced dead at the scene despite the efforts of paramedics.
Cambridgeshire Police said three teenage boys were arrested on Saturday night on suspicion of murder. All three have since been bailed.
A 14-year-old boy arrested at home in South Cambridgeshire has also been released on bail to return to Thorpe Wood Police Station in Peterborough on 20 February, the force said.
A second 14-year-old boy, who was arrested at his home in Cambridge, and a 17-year-old boy arrested at his home in South Cambridgeshire, have also been bailed to return to the same police station on the same date.
A post-mortem examination is due to take place on Wednesday.
Superintendent Adam Gallop, head of local policing for the south of Cambridgeshire, said: "We know there are a lot of people in the community who are talking about what has happened, including images and videos being circulated on social media.
"My plea is for parents and guardians to speak with their children and do the right thing by contacting us with information.
"I want to reassure the community that because they may have something on their phone, doesn't mean they are in trouble, but evidentially it could help our investigation."
Anyone with information should report it online, quoting Operation Helix, at www.cambs.police.uk/report. Those without internet access are asked to call 101.