The department conducted an initial internal investigation and then contacted the FBI on Wednesday. Because the case involves potential abuse of police power, Ballard said the case was referred to the federal agency.
All four officers, who were not identified, have been placed on restricted duty.
The officers have between three and 16 years of law enforcement experience, according to the department. They were all assigned to patrol a district that covers downtown Honolulu.
Honolulu Mayor Kirk Caldwell commended Ballard’s decision to hand the case to the FBI for review.
“Although these officers are presumed innocent, we need an independent agency to investigate exactly what occurred and whether these officers engaged in civil rights abuses,” Caldwell said in a statement. “Chief Ballard has promised to transform the Honolulu Police Department from a warrior mentality to a guardian mentality, and this is an approach to community policing that I wholeheartedly support.”