The FBI on Friday arrested former Transit Police sergeant David Finnerty, 47, of Rutland, for his alleged role in helping one of his underlings cover up the way that officer used a baton to beat a homeless man at the Ashmont T station - and then arrest the man for on a bogus charge for attacking him.

Finnerty faces a potential sentence of up to 20 years in prison if convicted on two counts of making false reports, the US Attorney's office in Boston says. His arrest comes several months after the Suffolk County District Attorney's office had agreed to drop its state case against him, after it said it found new computerized arrest-log data that showed Finnerty was not to blame.

Finnerty was an on-duty TPD supervisor when Officer Dorston Bartlett attacked the 32-year-old man and arrested him on the fake assault-and-battery charge, around 1:45 a.m. on July 27, 2018. Bartlett last year pleaded guilty to a reduced charge of assault and battery, rather than assault and battery with a dangerous weapon, civil-rights violation and filing a false police report, and was sentenced to probation.

According to the federal indictment, Finnerty "falsified an arrest report regarding the incident" by including falsified information and omitting key facts. The indictment does not detail the problems with the report. An account by the Suffolk County District Attorney's office on Bartlett's arrest in 2019 on state charges stated:

"In support of that charge [for the fake assault and battery on a police officer], Finnerty allegedly drafted a report that was submitted by Bartlett and ultimately approved by Orcel [another TPD supervisor]. Later the same morning, a member of the Transit Police command staff learned of Bartlett’s use of force and reviewed both a preliminary draft of that report and video from public safety cameras at Ashmont station. Based on his observations, he ordered the victim released from custody, charges did not issue, and the criminal investigation was launched."

But in October, 2022, DA Kevin Hayden's office submitted a nolle prosequi filing to drop the case after it said the new evidence came to light that disproved its earlier contention.

In a statement today, Transit Police Police Chief Kenneth Green said:

"We are thankful to the US Attorney’s Office and the FBI-Boston Division for their dedication and unbiased review of this matter. When the Suffolk County DA made the inconceivable decision to Nolle Prosequi this case we were astounded. I have always maintained since Hayden’s action if/when this matter was reviewed with an ethical and professional lens this would be the outcome. This indictment speaks for itself."

The Suffolk County District Attorney's office responded with its own statement:

"We've never tarnished the professionalism of our office by engaging in a critical back-and-forth on this matter and we're not going to start now. The decision to file a nolle prosequi in this case was based on our evaluation of state law, and our ethical obligations as prosecutors in light of our office receiving exculpatory evidence from the MBTA on the eve of Finnerty's trial. "