PITTSBURGH (AP) — Lawyers for the gunman who killed 11 people at a Pittsburgh synagogue requested a court order Tuesday to exhume the body of his long-dead father.

Robert Bowers' lawyers want the body exhumed for a DNA test after federal prosecutors raised questions about paternity during the penalty phase of Bowers' trial for the 2018 massacre at the Tree of Life synagogue.

Bowers, a 50-year-old truck driver from suburban Baldwin, was convicted in June on 63 criminal counts in the nation's deadliest antisemitic attack. A federal jury has to decide whether to sentence him to death or life in prison without parole.

The defense, trying to show that Bowers has a family history of mental illness, has introduced evidence that his father, Randall Bowers, was diagnosed with schizophrenia. The defense asserts Robert Bowers also has schizophrenia and opened fire at the synagogue out of a delusional belief that Jews were helping to commit a genocide against white people.

Randall Bowers died by suicide in 1979 on the eve of his own rape trial. At trial last week, prosecutors sought to cast doubt on whether he was Robert Bowers' biological father. The defense asked a judge on Tuesday to clear up the matter by ordering the exhumation of Randall Bowers' body.

“The Department of Justice presumably shares the defense’s concern with seeking the execution of a seriously mentally ill person. That the government is vigorously contesting, albeit on flimsy evidence, that Randall Bowers is the biological father of Robert Bowers indicates that it too believes that paternity matters and is significant,” wrote the defense, accusing prosecutors of seeking “to undermine the genetic basis” for Robert Bowers' mental illness.

Mental health experts hired by the previously defense told jurors that they diagnosed Robert Bowers with schizophrenia, a serious brain disorder whose symptoms include delusions and and hallucinations. A neurologist testifying for the prosecution disputed that Bowers has schizophrenia and said mental illness did not appear to play a role in the attack.

The defense, seeking to persuade the federal jury to spare Bowers' life, has been trying to show that Bowers had a deeply traumatic childhood marked by abuse and neglect, and that he threatened or attempted suicide multiple times in his teens, including by setting himself on fire. Prosecutors say Bowers was motivated by his hatred of Jewish people and spent six months planning the synagogue attack.

The government was expected to contest the defense motion to have Randall Bowers' body exhumed.