said a statement from David Welker, special agent in charge of the FBI's New Orleans office. "The affidavit remains under seal."

A search warrant was executed Wednesday at the department's homicide office, according to the FBI.

The New Orleans Times-Picayune, in a story published Friday, cited unnamed law enforcement sources as saying the agents seized the files and computer hard drives of two officers assigned to investigate police conduct in the bridge shooting -- Sgt. Arthur Kaufman and Sgt. Gerard Dugue.

Police Department spokesman Bob Young told the newspaper that federal agents were joined by investigators from the department's Public Integrity Bureau in executing the warrant. The Police Department "is cooperating with the U.S. attorney's office and the FBI in their continuing investigation into the Danziger Bridge incident," Young said in a written statement, the Times-Picayune reported. Young did not immediately return a call from CNN on Monday.

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

Seven police officers were initially charged in the case. They 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 some evidence contradicts that.

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

In August 2008, a judge 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.

In doing so, now-retired Criminal District Judge Raymond Bigelow noted that Bowen, Hills and Hunter were all forced to testify before the same grand jury that indicted them and the four others. Louisiana law says that information from a person's testimony cannot be used against them in a criminal case, the judge said. "The state improperly used the testimony of these officers to indict them as well as the others," Bigelow said. He cited testimony in which a police lieutenant said he had been shown Bowen's grand jury testimony.

In September, however, 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 Danziger Bridge incident.

"In the best spirit of law enforcement cooperation, and at the request of the victim's 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. "... 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."

Mary Howell, a New Orleans attorney representing Madison's family in a civil rights suit against city officials, said Monday she understands the Justice Department is investigating several incidents involving the Police Department in the days after Katrina, including the bridge shooting.

"It appears that they're serious, and hopefully they will be thorough," she said. "There's a lot that happened during that time that is not known now and frankly may never be known." She called the federal investigation the "best shot" at uncovering the truth.

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