An official said the video is consistent with what witnesses attending the service said about the actions of Devin Patrick Kelley during the massacre which left 26 people dead, eight of them children.
News of the grisly video emerged as authorities released an official list of the dead.
Eight male victims and 17 female victims ranging in age from one to 77 were on the Texas Department of Public Safety list which also includes the unborn baby of Crystal Holcombe, identified on the list as Carlin Brite "Billy Bob" Holcombe, age 0 and gender unknown.
The remaining eight victims were children and teenagers ranging in age from one to 16 years old.
Authorities said one of the children died at a San Antonio-area hospital. The remaining victims all died at the scene.
Details of the dead came after it became clear that authorities missed at least three opportunities that might have offered law enforcement a way to stop Kelley from having access to guns long before he slaughtered much of the congregation in the middle of the service in Sutherland Springs.
Police recovered a Ruger AR-556 rifle at the church and two handguns from the shooter's vehicle. All three weapons were purchased by Kelley, said Fred Milanowski, the agent in charge of the Bureau of Alcohol, Tobacco, Firearms and Explosives in Houston.
Kelley, 26, shot himself after a car chase by two local residents.