A former police chief of one of New York's largest counties pleaded guilty in federal court on Friday to beating a handcuffed suspect accused of stealing a duffel bag from his personal car, and then leading an attempt to cover it up.

James Burke, the top law enforcement officer in Suffolk County on Long Island until he stepped down in October, had served 31 years in the police force.

As part of a plea deal, Burke admitted to violating the civil rights of a Smithtown man and then leading an effort within the department to obstruct the probe into his actions. A federal investigation is ongoing.

"The defendant violated his oath and responsibilities as a law enforcement officer by exacting personal vengeance, assaulting a handcuffed suspect, and abusing his authority as the highest ranking uniformed member of the Suffolk County Police Department," said Robert Capers, U.S. attorney for the Eastern District of New York, on Friday.

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It was among a string of recent incidents in which law enforcement officers have been accused of using excessive force. While most of those cases have involved African-Americans and other minorities, the victim in Smithtown was a white man.

In December 2012, Christopher Loeb was accused of breaking into several cars, including stealing a bag that contained cigars, ammunition and other items from Burke's police car. Loeb filed a federal lawsuit against Burke and the county in February 2015.

In October, Burke resigned as police chief after a three-year federal probe. He was arrested last December. 

According to the federal grand jury indictment, Burke "slapped and punched" Loeb while he was handcuffed at a police station. Authorities said Burke and others then pressured detectives who witnessed the incident to conceal it.

Prosecutors secured the cooperation of 10 Suffolk County officers as part of their investigation, according to media reports. 

The U.S. attorney's office declined to comment on the probe. Burke's lawyer has not responded to calls for comment.

Investigators are examining the practices of the rest of the county's police department, which has more than 2,700 officers, and district attorney's office.