Policeman Keith Blakelock, who was stabbed more than 40 times, was nearly decapitated during the frenzied attack on the Broadwater Farm housing estate in the Tottenham district.
Nicholas Jacobs, 45, who was 16 at the time, was accused of being part of the mob that shouted "kill the pig" and set upon Blakelock as he tried to protect firefighters tackling a blaze during the riots.
Jacobs was charged last year with attacking Blakelock with a bladed weapon following an extensive police re-investigation into the murder.
In the public gallery, Winston Silcott, whose conviction for the murder of Blakelock was quashed in 1991, shouted "Yeah, yeah" and called out "Brother, brother".
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Among the witnesses were two people who admitted kicking Blakelock but were given amnesty from prosecution.
Other evidence presented to the court included a rap poem Jacobs wrote in custody about the murder.
The court heard that one witness had a long history of drink and drug problems. Another said he saw Jacobs use a machete, but under cross-examination, admitted he thought all black people looked alike.
In a statement, Blakelock's family said they hoped more people would come forward so some of those guilty could be brought to justice.
"We are obviously extremely sad and disappointed at the verdict," they said.
"We viewed this trial as an opportunity to see some form of justice served for Keith.
"There were many people involved... And it is regretful that no-one has yet to be found guilty despite the number of people with knowledge of the events."