Texas church gunman Devin Patrick Kelley was armed with three guns and had argued with his mother-in-law before the rampage, officials say.
The attack on the small church outside San Antonio during Sunday services left 26 people dead and 20 injured.
Kelley called his father after he was shot by an armed bystander and said he did not think he would survive. He was not legally permitted to own the weapons, which included a semi-automatic rifle and two handguns.
Freeman Martin, the regional director for the Texas Department of Public Safety, told reporters it appeared that Kelley died from a self-inflicted gunshot wound after first being shot by a “Good Samaritan”.
“This was not racially motivated, it wasn’t over religious beliefs,” Mr Martin said. “There was a domestic situation going on with the family and in-laws,” he said, adding that the mother-in-law had received threatening text messages from Kelley in recent days.