The gunman who killed 26 people at a church in the US state of Texas had a history of domestic violence and sent threatening text messages to his mother-in-law, according to authorities which said the shooting was not racially or religiously motivated.


The gunman, identified as 26-year-old Devin Patrick Kelley, wearing black tactical-style gear walked into the church and started firing from an assault rifle just after the Sunday morning service began at the First Baptist Church in Sutherland Springs.


Texas law enforcement officials said that the shooting was not racially or religiously motivated, rather it was connected to a "domestic situation going on within [his extended] family, which wouldn't be a first for him".


"We know that he expressed anger towards his mother-in- law, who attends this church," Freeman Martin of the Texas Department of Public Safety said, adding that the court- martialled former US Air Force airman had a history of sending her threatening texts. But his mother-in-law was not inside the church when Kelley sprayed bullets on worshippers.


However, the gunman's grandmother-in-law was present at the church when Kelley stormed in from the backdoor, firing all the way to the front and firing on his way back out of the church, authorities said.


He reloaded several times. He killed his grandmother-in- law during the attack, friends of the woman told the media. Authorities, however, also believe that the shooting was not a case in which suspect went to the church looking for his relatives but ended up killing many others.


"He was there to kill everybody. He is a mass killer of children and people ... he is a horrible monster," a source familiar with the matter told ABC News. The ages of the deceased range from 18 months to 77 years, authorities said.  -- PTI