The district attorney's office in New Orleans is considering whether to appeal a judge's decision to toss out murder and attempted murder charges against seven police officers for a shooting in the wake of Hurricane Katrina.

In quashing the indictments Wednesday, District Judge Raymond Bigelow agreed with defence arguments that prosecutors violated state law by divulging secret grand jury testimony to a police officer who was a witness in the case.

Survivors of the Sept. 4, 2005, shootings have said the officers fired at unarmed people crossing the Danziger Bridge to get food at a grocery store.

Ronald Madison, a 40-year-old mentally disabled man, and James Brissette, 19, were killed and four other people were wounded.

The officers admitted to shooting at people on the bridge, but said they were fired upon first.

Bigelow gave the district attorney's office until Sept. 18 to decide if it would appeal.

The office has already asked the U.S. justice department's civil rights division to look into the shootings, according to a letter the Madison family provided to reporters.

Testimony used against police improperly: judge

Bigelow also said that prosecutors had wrongly instructed the grand jury and that grand jury testimony by three of the officers was used against them improperly.

"It bordered on deliberate misuse of the law," the judge said.

The officers sat quietly on one side of the courtroom and didn't visibly react to Bigelow's ruling.

Following their indictment, one officer resigned from the police force, while the others were assigned to desk duty.

Bigelow ordered bracelets used to track the officers' whereabouts removed, but left in place the bail each paid until the district attorney decides what to do.

Police spokesman Bob Young said the officers would return to regular jobs quickly, but he was not sure where they would be placed.