A suspended Massachusetts State Police trooper who acknowledged breaking state ethics law by receiving free guns from a state-contracted firearms dealer has sued to get reinstated.

Robert Outwater has been suspended without pay since September 2016 when the allegations surfaced, The Boston Globe reported Tuesday.

He cooperated with a state investigation that led to charges against two other troopers. In exchange for his cooperation, the state attorney general's office agreed not to seek criminal charges against Outwater, although he acknowledged violating ethics law by accepting 10 guns from the dealer.

He sued state police last week to not only get his job back, but for back pay and a promotion to sergeant he says he would have received had he not been suspended.

Outwater has not been charged or convicted of a crime and has not been found guilty of any internal misconduct, and has been denied due process, his attorney, Patrick Hanley, said in a statement to the Globe.

He said that while serious, the allegations against Outwater pale in comparison to the misdeeds of some troopers still on the payroll, a reference to the agency's overtime abuse scandal.

State police spokesman David Procopio said the agency does not comment on pending litigation.