(CNN) - Tree of Life Synagogue shooting suspect Robert Bowers was arraigned in federal court Monday and pleaded not guilty to new hate crimes charges, a Justice Department spokeswoman said.
Prosecutors say Bowers used anti-Semitic slurs and criticized a Jewish group on a social media site in the days before he killed 11 worshippers last year in Pittsburgh.
Bowers, 46, allegedly shot and shattered a large window of the synagogue before he entered it.
Bowers pleaded not guilty in November to original charges.
Late last year, famed defense attorney Judy Clarke, who defended Unabomber Ted Kaczynski and Boston Marathon bomber Dzhokhar Tsarnaev, took over Bowers' case.
He was charged in a superseding 63-count indictment announced in January.
Thirteen hate crime charges were added to the new indictment, on top of obstruction of free religious exercise counts included in his original federal charges in October.