An 18-year-old gunman who killed 19 children and two teachers at a Texas elementary school barricaded himself inside a classroom, “shooting anyone that was in his way,” an official said Wednesday, describing the latest in a gruesome, yearslong series of mass killings at churches, schools and stores.

Police and others responding to Tuesday’s attack broke windows at the school in an effort to allow students and teachers inside to escape, Lt. Christopher Olivarez of the Texas Department of Public Safety said Wednesday on NBC’s “Today.”

Olivarez told CNN that all victims were in the same fourth-grade classroom at Robb Elementary School. Eventually, the shooter was killed by law enforcement.