Details continue to emerge about the day of the shooting at a Texas elementary school, including new accounts of how long the gunman was in the building, the time it took police to respond, and how the gunman was killed. The gunman entered the school at 11:33 a.m. Police had about 19 officers in the school at about 12:03 p.m. but did not enter the classroom where the shooter was located and kill him until 12:50 p.m., said Steven McCraw, director of the Texas Department of Public Safety, in a news conference Friday. Swipe right to see the timeline of the hour in which the shooter arrived at the school. Click the link in our bio to see the full timeline. USA TODAY is providing general details about the shooter to inform how mass attacks are often planned and carried out, particularly with respect to how weapons and targets are selected. These details give authorities and the public information that could help citizens spot future mass shooters and even prevent them.