A man arrested on suspicion of murdering the police constable Keith Blakelock in north London 25 years ago has been re-released on police bail.
Pc Blakelock was hacked to death on 6 October 1985 during the Broadwater Farm Riots in Tottenham, north London.
A man, originally from Tottenham, was held in February and questioned at Bury St Edmunds police station.
The 41-year-old suspect, who was 15 at the time of the attack, has been bailed to report back to police in November.
Two other men, aged 46 and 52, who were arrested at separate north London addresses in May, have also been questioned on suspicion of murder.
The pair, who lived in Tottenham in 1985, were released on bail until September.
Mr Blakelock, a father of three orginally from Sunderland, was murdered by a machete-wielding gang during clashes with police on the estate.
Six people were originally charged with the murder, including Winston Silcott, Mark Braithwaite and Engin Raghip.
The three men were convicted of the killing in 1987 but cleared on appeal four years later.
The riots, in which gangs attacked police, looted and set fires, were some of the worst the capital had seen for decades.
The officer and his colleague Pc Richard Coombes were attacked as they tried to protect firefighters as violence escalated.
The unrest was sparked by the death of Cynthia Jarrett, 49, who collapsed during a police raid on her home.
In 2005, police released images of Pc Blakelock's blood-stained overalls, with tape marks outlining the number of wounds inflicted upon him.
Investigators have repeatedly said people in the area have information about the identity of the killers they have not shared with police.