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 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.
One source said the man was arrested at Highpoint Prison, near Haverhill, Suffolk, but Scotland Yard refused to confirm or deny this.
