WASHINGTON — A former Boston police K-9 officer who helped in the response to the Boston Marathon bombing was sentenced Friday to 20 months in prison for attacking a Capitol Police officer with a chair during the Jan. 6 riot.

Joseph Fisher of Plymouth, Massachusetts, was sentenced after a court hearing in which he called his actions that day “an abomination.”

Fisher, 52, said he wanted to offer a heartfelt apology to the officer he assaulted, to the people of Washington, D.C., and to the country, saying his conduct was “egregious” and that he should’ve known better.

“Would you do this in your town?” Fisher said he would ask people he arrested who weren’t from the Boston area, adding that his actions on Jan. 6 disrespected the city of Washington, that he was highly embarrassed by what he did and that he stained his family’s reputation.

Federal prosecutors had sought 46 months of incarceration for Fisher, arguing that he was present during the early stages of the Capitol breach, and helped aid a Jan. 6 rioter’s escape.

“Upon entering the Capitol Building, Fisher made his way to the Capitol Visitor Center’s Orientation Lobby. At that time, another rioter sprayed a chemical irritant at a Capitol Police officer. The officer chased the rioter through a hallway in an attempt to apprehend him,” federal prosecutors wrote.

“Fisher grabbed a chair, watched and waited as the rioter and officer approached his position, and rammed the chair into the officer. Fisher then grabbed the officer and pushed him as another rioter shoved the officer from behind. The fight ended with Fisher on the ground and the other rioter successfully escaped,” they added.

Fisher was arrested in March 2023 and he pleaded guilty to all the counts he faced in February.

Fisher said Friday that he planned to continue with mental health counseling after he was released, along with spending time with his family.

Fisher was identified by online “sedition hunters” who have aided in the arrest of hundreds of Capitol rioters. Facial recognition surfaced many images of Fisher, including a screenshot from a video taken at a news conference after the capture of Dzhokhar Tsarnaev, one of the brothers who detonated two pressure cooker bombs at the Boston Marathon in 2013.

Fisher’s sentencing hearing unfolded when a judge in the same federal courthouse was sentencing a New Jersey man to 12 years in federal prison for assaulting officers while wearing a “MAKE AMERICA GREAT AGAIN” sweatshirt. Earlier in the day, a Florida man who online sleuths dubbed “Sedition Panda” because of the panda costume head he wore when he stormed the Capitol was convicted on all charges, including assaulting an officer.