The total number of charges against Robert Bowers is now up to 63, NBC News reported. In November, he pleaded not guilty to 44 charges, which included the murders.
Bowers also requested a trial by jury during his appearance at a federal courthouse in Pittsburgh on Monday, the report said.
Prosecutors say Bowers, 46, was armed with multiple weapons, including a Colt AR-15 rifle and three handguns, when he opened fire inside the Tree of Life Synagogue in the city of Pittsburgh’s Squirrel Hill neighbourhood on October 27 during a morning service.
The attack left 11 people dead and several others injured, including police officers who were trying to rescue victims and confront Bowers.