A man is fighting for life after he was attacked in south east London.
A short time later, officers were informed that a 20-year-old man had presented at hospital with head injuries and remains there in a critical condition, police said. His family are aware.
A 17-year-old male was arrested at the scene on suspicion of GBH.
He was taken into police custody and has been bailed pending further enquiries.
Police said on Monday morning a crime scene was in place and enquiries were ongoing.
Officers asked for anyone who witnessed the incident, or has information, video or images that could help police to call 101 or tweet @MetCC ref CAD 8860/29 Apr.
To remain 100% anonymous contact the independent charity Crimestoppers on 0800 555 111.