The suspected gunman in the Dallas Immigration and Customs Enforcement facility shooting had difficulty retaining a job, believed he had radiation sickness, and was a “loner,” according to his parents.

The suspect, Joshua Jahn, killed two ICE detainees and injured another when he targeted the Dallas field office from a nearby rooftop in late September. Bullet casings emblazoned with anti-ICE messages were found after the attack, which Homeland Security Secretary Kristi Noem said “was motivated by hatred for ICE.” Investigators haven’t determined a motive for the shooting.