ROSWELL, N.M. — It was supposed to be like any other day.

Students escaping New Mexico’s chilly temperatures congregated in the Berrendo Middle School gym before class started. Then, 13-year-old students Evan James and Kayla Koren, standing on opposite sides of the gym, heard a loud pop.

When they looked up, they saw blood and a fellow student on the floor, the victim of a gunshot wound to the face. A 12-year-old classmate holding a 22-gauge sawed-off shotgun stood nearby.

“I just saw blood everywhere,” Essance Sosa, 12, said Tuesday. “Everyone started screaming and running.”

Witnesses say that for the next 10 seconds or so, panic engulfed the gym and, eventually, the entire Roswell school Tuesday. Word began to spread that a student had opened fire, injuring a male and female student. Those who could, quickly texted parents and friends, and worried family members began frantically calling the school.

An 11-year-old boy was critically injured and a 13-year-old girl was in stable condition.

Officials credit John Masterson, an eighth-grade social studies teacher, with saving lives as he immediately stepped in and talked the boy into dropping his weapon. Masterson then held him until authorities arrived.

“He stood there and allowed the gun to be pointed right at him,” Gov. Susana Martinez told a packed room of 1,500 or so people at a prayer vigil late Tuesday, “so there would be no more young kids hurt.”

Officials also credit previous “active shooter” drills by Roswell Independent School District for preparing teachers and students, who say they were ready for what happened Tuesday morning. Students say they even thought the shooting was a surprise drill at first.

“I thought it was a drill. I really did,” James said. “Then, I realized it wasn’t.”

Investigators still aren’t sure why the boy, who has not been named by authorities or formally charged, opened fire. Authorities said the boy sneaked the shotgun onto campus through a bag or musical instrument case.

State Police Chief Pete Kassetas disputed a report from a hospital spokesman who said nurses treating the boy indicated he was the shooter’s target. He said a motive still is not known.

“We just don’t have a lot of information,” Kassetas told reporters late Tuesday.

The suspected shooter was transferred to an Albuquerque psychiatric hospital following a hearing Tuesday, according to attorney Robert Gorence, who is representing his family. Gorence said the family would release a statement Wednesday.