Thirteen year old Kimberly Macias cries as she sees schoolmates at a vigil for the victims, Tuesday, Jan. 14, 2014 in Roswell, N.M. A 12-year-old New Mexico boy drew a shotgun from a band-instrument case and shot and wounded two classmates at his middle school Tuesday morning before a teacher talked him into dropping the weapon and he was taken into custody, officials and witnesses said. (AP Photo/The Albuquerque Journal, Roberto Rosales) THE SANTA FE NEW MEXICAN OUT; MANDATORY CREDIT: ROBERTO ROSALES/THE ALBUQUERQUE JOURNAL

ROSWELL, N.M. - The 12-year-old boy who opened fire in a U.S. school gym warned some students away just before the attack, police said Wednesday.

New Mexico State Police Chief Pete Kassetas said the attack at Berrendo Middle School in Roswell was planned in advance. But he said it appeared the boy's victims — an 11-year-old boy and 13-year-old girl — were chosen randomly.

During a press briefing, Kassetas declined to speculate on a motive or say when charges would be filed. But he said the boy got the sawed-off shotgun from his family's home and had three rounds of ammunition.

Officials said Wednesday the 11-year-old boy who was shot in the face and neck remains in critical condition. The 13-year-old girl is in satisfactory condition with injuries to the right shoulder.

Kassetas said investigators worked through the night executing search warrants at the school, and determined from those searches that the attack was planned. They examined the boy's locker and the duffel bag the seventh-grader used to transport the 20-gauge pump shotgun to school.

Kassetas said the handle of the gun was sawed off so it had "more of a pistol grip."

The police chief added authorities had some indication that the boy verbally warned "select students" about the attack as he arrived at the school. He didn't elaborate.

When the shots first rang out in the school's gym, some students started laughing, assuming it was just another drill.

It wasn't. But those emergency exercises that students and teachers have undergone regularly for the past two years were being credited Wednesday with the quick disarming of the suspect.

The whole thing was over in 10 seconds, police say, thanks to John Masterson, a social studies teacher who stepped in and talked the boy into dropping his weapon. Masterson then held the boy until authorities arrived.

Police and schools across the U.S. adopted "active shooter" policies after two students in Colorado killed 12 classmates and a teacher at Columbine High School in 1999. Police waited 45 minutes for a SWAT team to arrive before entering the school. Officers now are trained to confront a shooter immediately.

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.

News from © The Associated Press, 2014