The Pittsburgh synagogue shooting suspect, Robert Bowers, said in court that he understood the charges against him and wanted to enter a "not guilty" plea; he was charged with 11 counts of murder.
The attack is estimated to have lasted 20 minutes. Robert Bowers walked through the Tree of Life synagogue, shooting at people in three locations.
The gunman was detained as he exited the building after being injured in a shootout with police.
US President Donald Trump has condemned the Pittsburgh synagogue shooting, saying there would be no tolerance for anti-Semitism following the attack.