Jurors in the murder trial of PC Keith Blakelock were told to set their emotions aside as they retired to consider their verdict.
Nicky Jacobs has been accused of stabbing the police constable to death during the Broadwater Farm riots in Tottenham, in October 1985.
Jacobs, 45, denies murdering the officer as he retreated with colleagues and firefighters during the riots, when he was just 16.
Summing up the case at the Old Bailey, Mr Justice Nicol described the police officer's murder as a "dreadful act".
But he told the jury of five women and seven men not to rely on their feelings about the killing when they retire to consider whether the defendant is guilty of murder.
Jacobs refused to give evidence during the trial and the judge said he was within his rights to do this.
Mr Justice Nicol told the jury they could draw whatever conclusions they thought appropriate from his decision not to take to the witness box.
Jacobs denies murder.