On the eve of the eighth anniversary of the war in Iraq, a federal judge in Chicago is handing a victory to hundreds of protestors who were arrested by Chicago Police during a march at the war’s outbreak in 2003.

Federal Judge Richard Posner says police acted “without justification” - and “perhaps in some panic” - when they arrested about 900 people at a downtown protest on March 20, 2003 - just a day after the start of the American invasion.

The city maintains they acted because marchers weren’t issued a permit, and wouldn’t disperse after police told them to. But Posner points out the city allowed the march to go ahead without a permit.

The law “does not permit the police to say to a person go ahead and march and then, five minutes later, having revoked the permission for the march without notice to anyone, arrest the person for having marched without police permission,” Posner writes in the decision.

John Stainthorp, a lawyer for the plaintiffs who also participated in the demonstration, said the ruling offers good news for protestors.

“If the police are … involved in controlling a demonstration, they must have objective basis to believe someone is breaking the law in order to arrest that person,” Stainthorp said.

The case now goes back to a lower court for trial.

The Chicago Police Department would not comment on the decision, and a spokeswoman for the Chicago Law Department didn’t respond to requests for comment.