Custodians at the Boston Public Library have routinely been paid for overtime hours they did not work, according to a library janitor who said he was terminated in July for leaving work early.

No other custodians were fired, but Calogero Russo told the New England Center for Investigative Reporting his firing has triggered a police investigation into the library’s overtime practices and the suspension of three senior managers.

He released an Aug. 18 letter he received from the state Department of Unemployment Assistance that appears to support his claim. The department approved Russo’s claim for unemployment benefits, saying “The claimant was discharged for falsifying their time card,” but “the rule was not uniformly enforced when it was violated by other employees.”

Several Boston unemployment attorneys cautioned it was unlikely the department had thoroughly investigated the library’s practices, as its hearing process is not a robust proceeding like a court case.

The Boston Herald first reported in late July that three library managers had been placed on administrative leave pending a police investigation, but the names of the managers and the subject of the investigation have never been disclosed.

An official from the Boston Police Department acknowledged that there is an ongoing investigation at the library but would not disclose the subject.

Library officials also refused to discuss the matter. "Due to an ongoing investigation by the Boston Police Department, the library cannot release any information pertaining to the allegations of this story until that investigation is complete,” said library spokeswoman Lisa Pollack.

The office of Mayor Marty Walsh also declined to comment for this story.

Payroll records obtained by NECIR show that along with Russo, three facilities officials were dropped from the library's payroll in late July: Michael Durfee the manager of central library custodians; Ralph Henry, the manager of library buildings; and Superintendent of Library Buildings James Meade. None of the three men responded to repeated phone calls, emails and letters seeking comment for this story.

Former Boston Public Library custodian Calogero Russo and his mother Joanne discuss his termination from the library, which they say was unfair Chris Burrell / New England Center for Investigative Reporting

Custodians at the central library get a lot of opportunities for overtime. About 40 Boston Public Library custodians racked up $355,000 in overtime last year, with 17 custodians earning more than 20 percent of their base pay in overtime. The top overtime earner on the custodial staff earned $32,929.49 in overtime on a base salary of $46,792.51. The custodians earned more in combined overtime than all of the other approximately 400 employees in the library system.

Asked in August about the high custodial overtime, library officials said the organization hosts many evening events at its various facilities — particularly after the 2016 completion of renovations at the Johnson building — requiring custodians to work overnight to clean up. WGBH News, NECIR’s reporting partner, has a broadcast studio space within the Boston Public Library.

Russo said it was standard practice for janitors to get paid for a full overnight shift — midnight to 8 a.m. — even if they did not stay for the entire shift. He said the practice was approved by senior managers.

“We were getting paid from 12 midnight to 8 in the morning,” Russo said in an interview Tuesday. “If we finished at 3 o’clock we would leave and we would still get paid until 8 a.m.”

Russo said this permission to inflate overtime only applied to private events — like weddings — held at the Copley Square library, where organizers pay thousands of dollars to rent the space. “It wasn’t the city’s money paying us,” Russo said. “It was the wedding’s money paying us the overtime.” But the overtime was logged on their city time sheets and appeared as part of their city payroll records.

“The policy should never be that if you are not there, then you still get paid,” no matter who is paying for it, said Matthew Cahill, executive director of the Boston Finance Commission, the city’s independent fiscal watchdog. “I don’t know what their policy is at the library, but if that is their policy, then they need to change that policy.”

Paul Craney of the Massachusetts Fiscal Alliance, a non-profit focused on government spending, said it doesn’t matter how the excess overtime was funded.

“It’s dishonest,” Craney said. “Someone somewhere is paying for it.… It shouldn’t be happening with city workers regardless who is paying for it.”

Russo has only worked at the library since 2016, but said the overnight overtime practice has been going on for years among dozens of janitors. He suspects he was singled out for punishment because he is battling a heroin addiction.

“I was fired for my addiction, and then they brought up all those other little charges to justify firing me, because they can’t fire me for my addiction alone,” he said.

A July 18 termination letter signed by library president David Leonard said Russo had come to work under the influence of drugs Apr. 3 and that he did not properly request time off in the following days. Russo confirmed he came to work high and then left work to get medical treatment for a wound and rehabilitation care.

Leonard wrote that Russo falsified his time sheets after returning to work during three nights in April and May. Russo said he was not the only one. He worked with a crew of custodians those nights, including a supervisor, and they all left at about the same time. Leonard declined to comment for this story.

Russo said he was called into a disciplinary meeting in May with a city human relations lawyer and his union representative and was questioned about leaving early. He said that was when he “kind of let the cat out of the bag” that it was a standard practice for night shift custodians to leave early, and that “Jim Meade gave us the OK to do it,” referring to the superintendent of library buildings who was dropped from the payroll in July. He said the other two supervisors who also were removed from the payroll system — Durfee and Henry — also oversaw custodians and approved their early departures.

That admission apparently triggered the police investigation and the suspension of the three managers, Russo said.

Jim Durkin, a spokesman for AFSCME council 93, the union that represents the custodians, would not discuss the case. “This is a pending disciplinary matter and we do not comment on pending matters,” he said.

Russo, who is now living with his family in Quincy, said he feels he was unfairly singled out. “It was 30 of us doing it. Why am I the only one getting in trouble for this?”

Paul Singer is investigations editor for WGBH News and its partner, the non-profit New England Center for Investigative Reporting.