The Uvalde mass shooting suspect bought more than 1,000 rounds of ammunition before opening fire and killing 22 people at Robb Elementary School, a law enforcement official said during a news conference on Friday. A U.S. soldier would take 210 rounds into combat.

The suspect had purchased 1,657 total rounds of ammunition – 315 rounds were found inside the school, said Steven McCraw, the director of the Texas Department of Public Safety.

A law enforcement source told CBS News that the amount of ammunition that the suspect brought with him is more than what an average U.S. soldier would go into basic combat with, apparently planning on a massive gun battle.

A magazine usually holds 30 rounds, and a U.S. soldier generally takes seven magazines – one in the weapon, and six spares – into combat.

Of the 315 rounds found inside the school, 142 were spent cartridges, or fired bullets, and 173 were live rounds, or unfired bullets, McCraw said. He also said 922 rounds were outside the school, but on school property, and of those, 22 were spent cartridges and 900 were live rounds.

Investigators found 60 magazines total – 58 in and around the school and at the site where the suspect crashed his car, and two at his residence.

During the news conference, McCraw gave a timeline of the suspect discussing his plans to buy a gun and shoot up the school. He asked his sister to help him buy a gun, but “she flatly refused,” McCraw said.

When asked how the 18-year-old suspect bought the expensive weapon, McCraw said he used a debit card. “Why and how is being looked at, and thousands of more leads are being looked at right now because we haven’t answered all the questions,” McCraw said.

McCraw also said the decision by the on-site commander at Robb Elementary School to delay breaching the classroom during the mass shooting was the “wrong decision.” Nearly 20 officers stood in a hallway outside of the classrooms during the attack for more than 45 minutes before agents used a master key to open a door and confront the gunman, McCraw said.

The on-site commander believed the suspect was was barricaded in a classroom and that the children were not at risk. “He was convinced at the time that there was no more threat to the children and that the subject was barricaded and that they had time to organize” to get into the classroom, McCraw said.

“Of course it was not the right decision. It was the wrong decision,” he said.

Teachers and children repeatedly called 911 throughout the attack. One girl pleaded: “Please send the police now,” McCraw said.

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