The federal trial of Robert Bowers, who killed 11 people at a Pittsburgh synagogue in 2018, began on Tuesday (May 30).
He faces the death penalty for 11 counts of hate crimes resulting in death and other charges.
He pleaded not guilty and his lawyers argued that he had a mental illness that made him believe he had to kill Jews to stop a genocide.
Prosecutors said he had a history of antisemitic posts and statements that showed his religious hatred. The trial is expected to last for weeks.