HONOLULU - Four Honolulu police officers are under federal investigation facing serious allegations while on the job.

Honolulu Police Chief Susan Ballard said the officers were responding to a 911 call involving a trespasser, when some of those officers allegedly forced the suspect to put his mouth on a public urinal.

The alleged incident happened Sunday in the Keeaumoku area.

One of the responding officers notified HPD command of what happened.

HPD investigated, found that victim and contacted the FBI on Wednesday.

The officers involved have been between three and 16 years years of service.

"If true, these allegations violate the core value of what HPD stands for. Our officers are sworn to uphold the rights of all persons and I expect every officer to treat every member of the public fairly and with respect. Personally I'm appalled," Honolulu police chief Susan Ballard said. 

Honolulu Mayor Kirk Caldwell issued a statement today saying "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."