A U.S. federal judge in New Orleans has sentenced four ex-police officers from 38 to 65 years in prison for killing unarmed civilians in the aftermath of Hurricane Katrina in 2005.

A fifth officer who did not take part in the killings but helped cover up the crime was given a six year sentence.

U.S. Assistant Attorney General Thomas Perez said the sentencing means New Orleans can take another step forward.

The officers shot and killed two people and wounded four after rushing to a bridge in New Orleans on reports of gunfire.

The police initially said they shot in self defense and claimed the victims had weapons.

Prosecutors said the civilians were unarmed and innocent. They said at least one of the officers planted a gun on one of victims as part of a cover-up.

Hurricane Katrina was one of the most destructive storms ever to strike the United States. It flooded nearly the entire city of New Orleans, leaving thousands homeless and causing hundreds of millions of dollars in damage.

Police say the chaos in the storm's aftermath brought countless reports of looting and gunfire, making it hard to discern true crime suspects from innocent bystanders.