A 17-year-old boy has been treated in hospital for stab wounds to the back after an attack in Essex that police described as "unprovoked".
The teenager was attacked in Brentwood on Friday evening and was taken to Broomfield Hospital in Chelmsford.
An altercation had occurred in a park on Church Lane at about 1745 BST, police said.
"This was a seemingly unprovoked attack which left a young man needing stitches," Det Con Sue Horswill said.
"It was still daylight when the incident happened so I'm confident that others in the park at the time, or passers-by will have seen something and will be able to help with our inquiries.
"We are extremely keen to hear from any witnesses to this incident so that we can piece together what has happened."