According to the officials, 26-year-old Devin Kelley opened fire on the church attended by his mother-in-law after he sent "threatening" text messages to her, the Independent reported.
Freeman Martin, the regional director for the Texas Department of Public Safety, said, "This was not racially motivated, it wasn't over religious beliefs. There was a domestic situation going on with the family and in-laws."
"We know that he expressed anger towards his mother-in-law, who attends this church," Martin added.
The U.S. officials said that he was not legally permitted to own the weapons.
According to the reports, Kelly possessed three guns.
The youngest victim of Sunday's shooting was an 18-month-old baby and the oldest one being 77-year-old.
After a brief chase, the law enforcement found the suspect dead of a gunshot wound inside his vehicle. Freeman Martin, a regional director with the Texas Department of Public Safety, said that the authorities were not sure if the wound was self-inflicted or the result of the resident who fired on the suspect.
Kelley, a former member of the U.S. Air Force, was court-martialled in 2012 on charges of assaulting his wife and child, the reports said. (ANI)