Phong Kieu (right), a teacher at the school, earlier named sister May Kieu as being one of the victims
Police have revealed that the two 15-year-old schoolgirls killed at an Arizona high school on Friday were in a relationship.
Glendale Police Officer Tracey Breeden also confirmed that the deaths were a murder-suicide, saying one girl shot the other, then took her own life.
Investigators said the teenagers' bodies were found on an outside the school's cafeteria with a gun and a suicide note nearby.
However, officers did not reveal any details of what the note said, and did not discuss what they believe the motivation for the killings may have been.
Officers also refused to name the pair, though school teacher Phong Kieu earlier named one of the victims as her sister, May Kieu.
Phong, who teaches science at the school, told ABC 15 she put on the news in her classroom after hearing about the shooting.
'We were watching the live footage and it first said two students,and after half an hour it said two female students, and then it said two sophomore students,' she said.
'My students were on their phones and were friends with her. And one of the students said it was May and her friend.
'That's when I called attendance and I asked for my sister's schedule. They put me on hold for 10 minutes and that's when I knew something was wrong.
'I was escorted from my classroom with one of the vice principals. He held my hand and told me we had to go upstairs. I walked up and I walked past so many people looking at me and they knew what happened.
'That's when they told me. My sister's gone. They confirmed it and she's not coming back.'
May and another 15-year-old sophomore student were found with gunshot wounds outside the school's cafeteria shortly before 8am this morning.
A gun was found next to the two bodies and police were not looking for a shooter.
Friends on social media posted tributes to May, calling her a 'beautiful angel'.
Yarelli Contreras wrote on Facebook: 'I will never forget the wonderful time I got to spend with May.'
She sent her condolences to the families of both dead girls, suggesting that the other girl killed was called Dorothy.
Other Facebook, Twitter and Instagram posts also paid tribute to May and Dorothy. The name of the second girl who lost her life has not been confirmed.
Police spokeswoman Tracey Breeden said police were called shortly before 8am (10am EST) and that officers were on scene within two minutes.
'They were able to locate two female students who are 15 years old. They were found by the main building under a covered area,' she said.
'They were deceased at scene. This is a tragic incident and we send our condolences to their loved ones.
'These two girls were found with a weapon besides them and we are not looking for suspects at this time.'
Breeden would not comment on whether police were investigating a murder-suicide, saying the investigation was at an early stage and the girls' relationship was unclear.
She added that there did not appear to be any other people near the cafeteria at the time and that no witnesses had come forward thus far.
'This was a tragic situation here today. We send out our condolences to the parents of these two young girls,' she said.
Police are in the process of notifying next of kin and have not released the names of the girls.
Dozens of police cars and fire crews were seen at the school on Friday morning following the shooting.
The school, which has around 2,000 students, was placed on lockdown but police told parents their children were safe and that they were dealing with an 'isolated incident'.
As many as 150 terrified parents gathered outside a nearby Walmart as they awaited news about their children.
One mother told ABC 15 that she had spoken to her son on the phone and that he was safe inside a classroom.
'He's safe in the room and he's OK. I thank God,' she said. 'He just said that they were trapped in a room.'
The 14-year-old sister of a student inside the school said: 'Right now we're just glad that most of the kids are safe.'
Another distraught mother said she was reading a story about the Columbine massacre when she saw police cars heading past her home.
She said one of her daughters had spoken to her but she has not heard from another. She was considering keeping her girls home from school in future
'I can't imagine having to drop them off at school next week,' she said.
A spokesman for Glendale Union High School District said: 'Independence High School was put on lock down this morning due to a police investigation. Police have secured the campus. There is no active shooter on campus. The investigation is ongoing.
'The campus remains on lock down and no one will be allowed to enter or exit the campus until the police have lifted the lock down and ensured the safety of the school.
'Parents will be notified as soon as it is safe for students to be picked up from campus.'
Glendale Mayor Jerry Weiers tweeted: 'Our hearts go out to everyone at Independence High School this morning. We are standing by for information.'
Two 15-year-old schoolgirls shot dead in murder-suicide at Arizona high school were in a relationship Chris Pleasance and Ollie Gillman and Regina F. Graham 13 February 2016Tweet