The suspected gunman believed to have killed at least 26 people at a Texas church has been named as Devin Patrick Kelley, a former member of the US air force who received a court martial for assault on his wife and child five years ago.

Axar.az reports citing the Guardian that the 26-year-old reportedly entered the wooden-framed First Baptist Church on Sunday dressed in black tactical-style gear, a ballistic vest and carrying an assault rifle. He shot victims ranging in age from five to 72 years old, including a pregnant woman and the pastor’s 14-year-old daughter.

Air force spokeswoman Ann Stefanek said records showed Kelley joined Logistics Readiness at Holloman Air Force Base in New Mexico in 2010.

She said he was court-martialled in 2012 for “assault on his spouse and child” and spent a year in a military prison and was given a reduction in rank. In 2014, Kelley received a bad conduct discharge, she added.

Kelley has not been formally named as the suspect. However, two officials, including one working in law enforcement, identified him as the alleged killer on the condition of anonymity to the Associated Press. He was also named by the New York Times and multiple other US outlets citing sources.

Investigators were looking at social media posts Kelley made in the days before Sunday’s attack, including one that appeared to show an AR-15 semiautomatic weapon, the rifle used in the massacre.

No motive has been declared for what the state governor, Greg Abbott, called the worst mass shooting in Texas history. It is not clear if Kelley had links to any militant groups.

Authorities described a white man in his 20s who pulled into a gas station across from the First Baptist Church around 11.20am on Sunday. He crossed the street and started firing the rifle at the building before entering and killing worshippers.