Police investigating the murder of two French students in the brutal knife attack in London have made a second arrest. A Metropolitan police spokesman said a man surrendered himself at a south London police station and had since been taken to hospital for treatment to injuries.

"A 33-year-old man handed himself in at a south London police station early this morning where he currently remains in custody," Scotland Yard police said in a statement.

This follows the arrest of a 21-year-old man on Saturday in connection with the murders over the weekend. The detainee was freed without charge the next day.

Police released no other details about the latest suspect. Nor did they offer any straightaway explanation about why the first suspect was let out.

Police have released an e-fit - computer-generated likeness - of a man who was seen running away from the surroundings of the apartment on the night of the crimes. The suspect is a white male, aged 30 to 40 and slim. He was wearing a light-colored baseball cap, dark top, blue jeans and white trainers.

The badly burned bodies of graduate bio-chemistry students Laurent Bonomo and Gabriel Ferez, both 23, were discovered a week ago in a burned-out London apartment by firefighters after responding to a fire call. Initially, they believed that Bonomo and Ferez died in the fire, but post-mortem exams indicated that they had been bound, gagged and died of multiple stab wounds to the head, neck, torso and back. Results showed 196 stabs to Bonomo’s body, with up to 80 of the wounds inflicted after he was dead, while Ferez’s received 47.

London detectives believe their bank cards and two Sony PSP games consoles were the motive for the double murder.

Both men were in the third year of a masters degree at Polytech Clermont-Ferrand in central France and were in London because they had been chosen to participate in a research project at Imperial College and were scheduled to go back home within weeks.