A Plymouth police sergeant was charged in federal court Tuesday with physically abusing an arrestee last November and falsifying police reports to cover up the abuse, according to the office of US Attorney Carmen M. Ortiz. The indictment of Shawn Coughlin, 45, of Plymouth alleges that Coughlin struck the handcuffed arrestee in the head and kneed him in the body, both acts that Coughlin omitted from the reports, the statement from Ortiz’s office said. According to the indictment, Coughlin falsely stated in police reports that the arrestee “continued to resist by attempting to kick at the officers present . . . while still screaming obscenities and various threats.”Melanie Dostis can be reached at email@example.com.