According to prosecutors, 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 neighborhood on 27 October during a morning service.
The gun attack killed 11 people while injuring several others, including police officers at the scene.
The total number of charges against Robert Bowers stand at 63, according to US-based media reports. In November 2018, Bowers pleaded not guilty to 44 charges, including the murders.
The 2018 Pittsburgh shooting is reportedly the deadliest attack on a Jewish synagogue in the United States.