A man has been arrested over the murder of Pc Keith Blakelock during the 1985 Broadwater Farm riots.
A 40-year-old former Tottenham man was questioned at Bury St Edmunds police station in Suffolk over the killing.
A Metropolitan Police spokesman said the suspect was held on Friday and released today on bail until May.
Mr Blakelock, a father of three, was murdered by a machete-wielding gang 20 years ago during riots in Tottenham, north London.
The officer and his colleague, Pc Richard Coombes, were attacked as they tried to protect firefighters as violence spiralled.
The unrest was sparked by the death of Cynthia Jarrett, 49, who collapsed during a police raid on her home.
Winston Silcott, Mark Braithwaite and Engin Raghip were convicted of the killing in 1987 but cleared on appeal.
Five years ago police released images of Mr Blakelock's blood-stained overalls in a bid to provoke witnesses come forward.
Investigators have repeatedly said people in the area have information about the identity of the killers they have not shared with police.
The police spokesman added: "Officers from the Metropolitan Police service's Homicide and Serious Crime Command arrested a 40-year-old man on suspicion of the murder of Pc Keith Blakelock in Suffolk on Friday, February 5.
"The man, originally from Tottenham, was taken to Bury St Edmunds police station where he was questioned.
"This year marks the 25th Anniversary since Pc Blakelock was murdered during the Broadwater Farm Riots on October 6, 1985.
"Police would like to reassure anyone who has information regarding those involved in the murder of Pc Keith Blakelock or the attempted murder of Pc Richard Coombes, who was also attacked that night, that they can contact the incident room in confidence on 020 8733 4613."Reuse content