GLENDALE, Ariz. (Reuters) - Two 15-year-old girls who were believed to have been romantically involved were found shot dead on Friday at an Arizona high school in an apparent murder-suicide that initially triggered a security lockdown of the campus, police said.

The pair, whose identities were not made public, were both 10th-grade students at Independence High School in the Phoenix suburb of Glendale, and a suicide note was recovered from the scene of the shooting, according to a police statement.

After a report of gunfire at the school, the two girls’ bodies were found near the cafeteria under a covered patio, each having sustained a single gunshot wound, and a weapon was discovered nearby.

Although the incident remained under investigation, evidence from the scene has led homicide detectives to determine that one of the girls apparently killed the other before taking her own life, and that no other students witnessed the shooting, police said.

“Information gathered by detectives reveals the two girls were very close friends, appearing to also be in a relationship,” and no other suspects are being sought, the police statement said.

“The investigation has led detectives to believe this incident was a murder-suicide,” it added.

Glendale police spokeswoman Tracey Breeden said the school was placed on lockdown after the shooting, and the street in front of the campus was also shut down.

Students, meanwhile, posted updates on social media from their classrooms as dozens of anxious parents, who were barred from the campus, gathered in the parking lot of a nearby Wal-Mart store to await their children.

Jasmine Molina, 15, was in English class when the lockdown was declared.

“I never thought it would happen here. This tells me that it could happen anywhere, at any school, even if it’s a good school,” said Molina, who was holding a stuffed bear her boyfriend had given her that morning for Valentine’s Day.

Ana Lisa Romero, whose son, Lalo, attends the school, said in a Facebook message to Reuters, “I am going crazy just thinking that could have been my son or nieces or nephews.”

Public officials expressed condolences over the shooting.

“Our hearts remain with the students, educators and families of Independence High School and the entire Glendale community,” Arizona Governor Doug Ducey said in a statement.

Independence High, which is just a couple miles outside Phoenix, has about 2,000 students, school district representative Sara Clawson said.