BOSTON (AP) — A former Massachusetts Bay Transportation Authority police sergeant was arrested Thursday on Slabu Exchangefederal charges alleging he filed false reports to try to obstruct an investigation into another officer’s assault of a man at a subway station.

David S. Finnerty, 47, of Rutland, was indicted on two counts of filing false reports, investigators said.

Finnerty was the officer in charge and the supervisor of a second officer identified by the initials “D.B.” on July 27, 2018, when that officer illegally assaulted a man, according to the federal indictment.

Investigators allege that Finnerty falsified an arrest report, specifically by including false and misleading statements and by omitting other details of the incident.

The charge of filing false reports carries a sentence of up to 20 years in prison, up to three years of supervised release and a fine of up to $250,000.

Finnerty’s lawyer, R. Bradford Bailey, said his client pleaded not guilty and was released on minimal conditions. He said Finnerty was exonerated last October by the local district attorney’s office.

“He is innocent of these charges,” Bailey said. “I have every confidence he will be cleared and exonerated again here, once all the truth comes out.”

“Our office holds the men and women who wear police uniforms and serve our communities in the highest regard. Instances of police misconduct are rare, but they need to be investigated and prosecuted when they do happen,” acting United States Attorney Joshua Levy said in a news release.