The video makes clear that the masked man clad in black stormed into the church intent on shooting everyone there — and he nearly did. For several minutes, he fired quickly, pausing only to reload, methodically shooting his terrified victims — including small children — in the head, execution-style.

A video camera captured the blood bath inside a rural church, law enforcement officials said on Wednesday, recording the worst mass shooting in Texas history, which left 26 people dead, 20 wounded, and a small town devastated. That gruesome footage, which state and federal investigators have reviewed, stemmed from the church’s practice of regularly recording its services and posting the videos online.

Law enforcement agencies declined to say whether they would ever publicly release the video, which shows that the shooting lasted about seven long minutes, said an official who was briefed on the matter, speaking on the condition of anonymity because the investigation is continuing. The official said that the killer, armed with an assault rifle, went to the First Baptist Church in Sutherland Springs on Sunday morning with magazines capable of holding more than 400 rounds of ammunition, but it is not clear how many shots he actually fired.

On Wednesday, the Texas Department of Public Safety released the names of the dead, a cross-section of this unincorporated village of a few hundred people southeast of San Antonio. They included 10 women, seven men, eight children, and the fetus carried by one of the victims, Crystal M. Holcombe. The youngest of the children was 1; the oldest of the adults was 77.