On December 10, members of the First State Violent Fugitive Task Force attempted to arrest 37-year-old Evelio Rivera in Rehoboth Beach.
Rivera, of Reading, Pennsylvania, was wanted for an attempted murder charge.
Investigators say Rivera opened fire, shooting Senior Corporal Timothy Webb at least six times.
Webb - along with two other officers - fired their weapons, killing Rivera.
Webb survived after nearly a week in the hospital.
In findings released Friday, the Department of Justice found the task force officers' use of force was justified and necessary to protect themselves and others.