Two men have been arrested on suspicion of murdering Pc Keith Blakelock in north London 25 years ago.
The men, aged 52 and 46, were arrested at separate addresses in north London on Friday at 0800 BST.
Police said the men, originally from Tottenham, were taken to a north London police station for questioning before being released on bail.
Pc Blakelock was hacked to death on 6 October 1985 during the Broadwater Farm riots in Tottenham.
A Metropolitan Police spokesman said the two men were arrested by the service's homicide and serious crime command.
They were interviewed and have been released on bail until September.
Pc Blakelock, a father of three, originally from Sunderland, was murdered by a machete-wielding gang as about 500 youths rioted on the estate.
The riots, in which gangs attacked police, looted and set fires, were some of the worst the capital had seen for decades.
Pc Blakelock and his colleague Pc Richard Coombes were attacked as they tried to protect firefighters as the violence escalated.
In 2005, police released images of Pc Blakelock's blood-stained overalls, with tape marks outlining the number of wounds inflicted upon him.
Winston Silcott, Mark Braithwaite and Engin Raghip were convicted of the killing in 1987 but were cleared on appeal in 1991.
A new murder investigation began in 2003.
Investigators have repeatedly said people in the area have information about the identity of the killers they have not shared with police.