A former police officer who gunned down an unarmed, mentally disabled man at the foot of a New Orleans bridge after Hurricane Katrina testified Wednesday that he feels horrible about the shootings, but maintained his actions were justified.

Robert Faulcon, one of five current or former officers on trial for charges stemming from the Danziger Bridge shootings, also said he believes other officers engaged in a cover-up.

Faulcon said he thought 40-year-old Ronald Madison was armed and posed a threat as he chased him down the west side of the bridge. He said he became "paralyzed with fear" when he saw Madison — bent over with his hands tucked into his body — turn toward him, looking over his left shoulder.

"The fear you have in that split-second, there's no words to describe it," he said.

Prosecutors say Faulcon had no justification for shooting Madison in the back with a shotgun as he and his brother, Lance Madison, ran from police.

Faulcon didn't dispute that neither brother was armed, but he insisted he saw two other residents with guns on the east side of the bridge, where police shot five people, killing one in 2005.

Faulcon balked at giving a "yes" or "no" answer when Justice Department attorney Bobbi Bernstein asked him if police officers are allowed to shoot somebody whom they merely suspect or presume to be armed.

"It's so many scenarios and so many circumstances you have to take into account to make that decision," he said.

Police shot and killed Madison and 17-year-old James Brissette and wounded four others on the bridge on the morning of Sept. 4, 2005, less than a week after Katrina's landfall.

Prosecutors say police fabricated witnesses, falsified reports and planted a gun to make the shootings appear justified.

Faulcon, who resigned from the police department less than a month after the shootings, denied participating in a cover-up. But he said police reports on the shootings contained numerous false statements about what he saw and did on the bridge.

The reports, for instance, say Faulcon saw Madison reach into his waistband before he shot him. Faulcon said he never told that to any of the police investigators. He also denied saying he saw Lance Madison throw a gun off the bridge or that he had "returned fire" after being shot at, as the reports stated.

"Do you agree that there was a cover-up in this case?" Bernstein asked.

"Based on what I've learned now, yes," Faulcon said.

Sgt. Arthur Kaufman, who was assigned to investigate the shootings, is charged in the alleged cover-up.

Faulcon was one of several officers who piled into a rental truck and headed to the bridge in response to an officer's distress call. He said he was in the rear of the truck and heard gunfire on the way to the bridge.

"I assumed we were getting shot at as we arrived," he recalled.

Faulcon said he shouted, "Police!" as he jumped out and saw a fellow officer firing toward people on a walkway behind a concrete barrier. Faulcon said he fired at least four shotgun blasts in the same direction because he saw guns on two of the people on the walkway.

"If I had known they weren't armed, I never would have fired my weapon," he said.

Faulcon conceded nobody on the walkway pointed a weapon at him and said he never saw any civilians on the bridge fire a weapon.

During cross-examination, Faulcon said he didn't order Ronald Madison to stop or identify himself as a police officer because it "gives away your location" — and he feared for his life.

Faulcon also said he was worried that he and a Louisiana State Police trooper were walking into an ambush after he saw Lance Madison run ahead of his brother and disappear into a motel parking lot.

Faulcon defended his actions but expressed remorse.

"I feel horrible," he said. "My heart goes out to the people that were hurt."

Faulcon was the first defendant to testify at the trial, which began more than four weeks ago.