NEW ORLEANS, Louisiana (CNN) — Federal authorities will conduct an investigation into the shootings of unarmed civilians, allegedly by seven police officers, on a New Orleans bridge in the aftermath of Hurricane Katrina, officials said Tuesday.

In August, a judge dismissed state charges against the seven, six of whom are still police officers.

The Department of Justice’s Civil Rights Division, the U.S. Attorney’s Office for the Eastern District of Louisiana and the FBI’s New Orleans office issued a statement saying they plan to conduct “an independent and thorough review” of the incident on the Danziger Bridge.

“In the best spirit of law enforcement cooperation, and at the request of the victims’ families, the New Orleans district attorney has referred the matter to the United States Department of Justice for review,” Jim Letten, U.S. attorney for the Eastern District of Louisiana, said in the statement. “As the result of this productive dialog and referral to us, the Civil Rights Division, FBI and our U.S. attorney’s office will utilize as much time and resources as necessary to determine whether there are any prosecutable violations of federal criminal law in this matter.”

The shootings occurred September 4, 2005, just after Hurricane Katrina slammed into the Gulf Coast. Two men were killed and four were wounded as they were attempting to evacuate by crossing the Danziger Bridge over the Industrial Canal in eastern New Orleans.

The seven initially charged in the case were responding to reports that rescue workers had heard gunfire and that an officer had been wounded on the bridge. Police have said officers fired shots only after being shot at, although evidence contradicting that assertion was presented.

Killed were Ronald Madison, 40, and James Brissette, 19. Autopsy results showed that Madison, a mentally ill man who had no criminal record, was shot in the back. No weapon was found on or near his body.

In August, Criminal District Judge Raymond Bigelow quashed indictments against Sgts. Kenneth Bowen and Robert Gisevius Jr., Officer Anthony Villavaso II and former Officer Robert Faulcon Jr., who were all facing first-degree murder and attempted murder charges. In addition, he threw out attempted first-degree murder charges against Officers Mike Hunter Jr. and Robert Barrios, and attempted second-degree murder charges against Officer Ignatius Hills.

Bigelow noted that three of the defendants — Bowen, Hills and Hunter — were forced to testify before the same grand jury that returned indictments against them and the four others. Louisiana law, the judge said, says that information from a person’s testimony cannot be used against that person in a criminal case.

“The state improperly used the testimony of these officers to indict them as well as the others,” Bigelow said. The judge cited testimony in which a police lieutenant said he had been shown Bowen’s grand jury testimony.

Letten’s statement said that in order to ensure “the integrity of the process,” no additional comments would be made until the federal review is complete.