A St. Louis police timeline provided on Monday showed officers shot and killed the suspect in the Central Visual and Performing Arts High School shooting within 10 minutes of arriving at the school — which probably saved lives.

The 19-year-old shooter was carrying an AR-type rifle and more than 600 rounds of ammunition, Fox News reports. Officers found cartridges and shell casings when they entered the building, police say.

According to the narrative released Tuesday, responding officers were helping Collegiate students evacuate when they heard shots being fired at Central VPA. They eventually found the suspect barricaded on the third floor in a classroom used by CVPA. Officers fired their weapons when he refused multiple commands to drop his weapon and surrender, police said.

A student and a gym teacher were killed in the attack, St. Louis Public Radio reports. The injured, all teenagers, were reported to be stable with gunshot wounds, cuts and broken bones. One victim, a 15-year-old boy, required surgery.