HONOLULU -- The head of the city department whose employees are under criminal investigation for an overtime scam said he has changed procedures to avoid future fraud.

A supervisor and four city street sweepers are accused of getting paid overtime for weekend shifts they never worked, KITV first reported.

City employees complain that employees in the city's road division have routinely padded their overtime checks and taxpayers pay them for extra work they never carried out. One supervisor is on leave with pay while he is being investigated, but four other employees are still on the job.

Four city street sweepers have admitted to the scam in which they were paid overtime for weekend shifts they did not work and then kicked back some of the cash to supervisor Manuel Castro, officials said.

In March, police arrested Castro on suspicion of theft, bribery and tampering with a government record and released him without charges pending further investigation.

The scheme continued for more than one year, sources told KITV.

"I don't want to speculate on why it festered for so long. I'm new to the department," city Facilities Maintenance Director Jeoffrey Cudiamat said.

Cudiamat took over the city's Facilities Maintenance Department as director at the end of January. Last month, he began new policies to curb overtime throughout the department, which also handles repaving and repairing roads.

"When I came on board, we instituted these policies because we realized that overtime was rampant in our department," Cudiamat said.

Road crews now must have overtime approved in advance -- something that was not required before.

"We have instituted a policy internally for them to request and for the supervisors to evaluate the work that's being done after they perform the overtime. So, we are scrutinizing it at every level," Cudiamat said.

He said overtime bills have decreased since the new policy took effect. Some city yards have seen OT drop by as much as 60 percent, Cudiamat said.

"I'm happy to see some of the numbers come down and see that we are paving more roads now and see that we are using less overtime," the director said.

While the police overtime investigation continues, the city is conducting an internal investigation and has also hired a private investigator to look into the situation.

Because of a hiring freeze, the Facilities Maintenance Department has about a 30 percent vacancy rate -- about 230 unfilled positions. It has requests pending to fill 32 of those open jobs, which would help cut down on the need for legitimate overtime.