The report notes a large tumor known as a meningioma was found during the autopsy.
Authorities say 68-year-old Thomas Matusiewicz killed himself following the courthouse shooting Feb. 11. His widow, Lenore Matusiewicz had sought an independent autopsy saying she believes an untreated brain tumor was to blame for her husband's actions.
Matusiewicz, a former New Jersey police officer, was cremated shortly after his body was released by the state. The Delaware attorney general's office had initially refused to allow the release of the autopsy to the family, citing an ongoing investigation.
The shooting capped a lengthy custody battle between Matusiewicz' son and his ex-wife.