PHOENIX (Reuters) - The handgun used in last week’s apparent murder-suicide of two 15-year-old girls found shot dead at their suburban Phoenix high school was furnished by a fellow student at the request of one of the girls, police said on Tuesday.

Sergeant David Vidaure, a spokesman for the police department in Glendale, Arizona, said the girl had obtained the weapon from her classmate, a 15-year-old boy, on the eve of last Friday’s fatal shooting after telling him “she needed it for protection”.

The classmate obliged by providing the girl with “a family-owned handgun, from his home, without the permission or knowledge of his parents,” Vidaure said in a statement.

Suicide is the third-leading cause of death among American youths aged 10 to 24, resulting in 4,600 lives lost each year, and firearms are the most common method for taking one’s own life, according to the U.S. Centers for Disease Control and Prevention.

The male student has been cooperating with detectives, though his involvement will be reviewed by the Maricopa County Attorney’s Office for possible charges, Vidaure said.

Neither the two girls nor their classmate - all students at Independence High School in Glendale - have been publicly identified because all three are minors.

Although the precise circumstances remain under investigation, evidence from the scene has led homicide detectives to determine one of the girls killed the other before taking her own life, and that no other students witnessed the shooting.

The two girls were believed to have been very close friends and romantically involved.

Their bodies, a suicide note and the pistol were found in a canopied patio area near the school cafeteria after gunfire erupted shortly after classes started, triggering a security lockdown of the campus as police initially searched the school grounds for suspects.

No surveillance video of the incident was captured, police said.

On Tuesday, counselors and social workers were brought to the 2,000-student high school to help those returning to class for the first time since the incident.

In a Facebook message to parents and guardians, school principal Rob Ambrose offered condolences to the families of the two girls and acknowledged the outpouring of community support.