The family of Pc Keith Blakelock said they were "extremely sad and disappointed at the verdict" following the acquittal of Nicky Jacobs.
A jury took just six hours to clear the 45-year-old of the murder of Mr Blakelock who was stabbed over 40 times in an attack at Broadwater Farm in 1985.
"We are obviously extremely sad and disappointed at the verdict. We viewed this trial as an opportunity to see some form of justice served for Keith," a statement on behalf of the family said.
"There were many people involved in a murder on that night of 6 October 1985 and it is regretful that no-one has yet to be found guilty despite the number of people with knowledge of the events of that night."
The family, who thanked everyone involved in ensuring the case was brought before a jury, said they hoped more people would come forward to bring those responsible to justice.