More than a third of cases investigated by a D.C. police oversight board after complaints were made about officers' conduct this past year involved officers who did not properly use their body-worn cameras during those incidents, according to a report made public Tuesday.

Some officers turned the cameras on too late, others too early, the report from the Office of Police Complaints found. In 13 percent of the cases, at least one officer at a crime scene or incident failed to turn on the camera, though colleagues did.

Michael G. Tobin, the director of the Office of Police Complaints, said that part of the noncompliance with the cameras "is unintentional and can be attributed to the time it takes to adapt to any new technology."

But he said that his investigators have sometimes been hampered by the lack or poor quality of video linked to an officer's "failure to follow policy" on operating the cameras. "Sometimes the failure of an officer to activate the camera has a negligible effect if other cameras in the vicinity are activated, and sometimes the failure means the entire case may be compromised," Tobin said.

Tobin said his agency's findings, released in an annual report covering fiscal year 2017, should move police toward imposing sanctions on officers who fail to properly activate the recording devices. "Having cameras on every officer will mean nothing if the department fails to enforce the policy mandating their use," Tobin said in an email.

Dustin Sternbeck, the police department's chief spokesman, called the report's conclusion of body camera misuse "misleading." He noted the largest category of improper use was instances where officers failed to notify people they were being recorded.

Police rules require notification only when practical, which is not in many encounters that unfold in an instant, Sternbeck noted.

"OPC does not indicate whether it was practicable in these cases or whether the notification may have been given prior to the recording beginning," Sternbeck said in a statement.

He also took issue with the report faulting some recordings for having obstructed views and said more context is needed. "There is no additional information to determine if the obstructions were avoidable or were the result of the physically rigorous work that police officers often are required to do," the statement says.

Sternbeck said the department "takes the failure to activate a camera very seriously, and we have worked with our officers who have readily accepted this technology to ensure that the cameras are activated when necessary."

The report says the complaint office investigated 773 cases in fiscal 2017, up 77 percent from 438 the previous year. That rise was, in part, driven by a new online filing process and an extended period of time that people now have to register a complaint.

The Office of Police Complaints is an alternative to the police department's in-house investigation squad, the Internal Affairs Bureau. The civilian board typically investigates allegations of improper use of force, bad language and rude behavior and makes recommendations on disciplining individual officers and on broader policy concerns.

Investigators also monitored the police handling of large demonstrations, including the unrest on Inauguration Day. And the board gained new authority this fiscal year to audit police files on use of force. Nearly half the cases investigated in fiscal 2017 involved allegations of police harassment, and more than a quarter involved complaints of inappropriate language or conduct. Complaints over use of force made up 10 percent of the cases, slightly down from last year.

The report says the office closed 440 investigations, which include those filed the previous year. About 40 percent were dismissed with no credible merit found, down from roughly half to two-thirds dismissed in the previous three years.

Complaints against officers were sustained in 3 percent, or 14 cases, about on par with previous years. One complaint involved use of excessive force, dating to 2014. Punishment on cases decided this year ranged from re-education to letters of reprimand. The cases do not include those handled by detectives in the department's Internal Affairs Division, which can involve more serious allegations.

About 2,800 officers, mostly in patrol, wear body cameras. The department implemented the program slowly, with about half the eligible officers equipped with recording devices in the summer of 2016. All the officers had cameras by December 2016. The police complaints office said that camera footage was relevant in about 63 percent of the 773 cases it investigated.

The report notes a problem of delays in officers activating the cameras — though the devices constantly record and save one minute of already recorded footage once the officer hits the record button. This notably happened on Sept. 11, 2016, when an officer failed to turn on his camera until after he fired his gun in a confrontation with motorcyclist Terrence Sterling, who was killed. The officer did not face criminal charges and is undergoing an internal investigation.

Police Sgt. Matthew Mahl, the chairman of the police union, said he plans to ask the department for new equipment that would automatically turn on body cameras when a gun is removed from the holster.

In an interview last week, Tobin said the board's analysis largely falls in line with a study completed by a D.C. police in-house research team that showed officers wearing cameras reported using force about as often as officers who didn't have them.

He said that given police departments are under increased scrutiny, failure to properly use a police body camera could result in an assumption by the public that it was intentional, "and the officer's credibility will be questioned as to the entire incident."