Police in Arizona said they arrested a 16-year-old student who threatened in an online video to "kill everyone" at her high school, then kill herself. The teenager was a student at Red Mountain High School in Mesa, a suburb of Phoenix, the office of Maricopa County Sheriff Joe Arpaio said. "The threat was posted on a YouTube channel owned by a transgender community in Toronto, Canada," it said. The channel owner contacted Toronto police, who tracked the person that posted the video. Canadian police then contacted the sheriff's office late on Wednesday, and within three hours they were able to find the suspect's home in Mesa. Detectives went to the home, questioned the teenager in the presence of her parents, then arrested her early on Thursday "after she admitted to posting the threat". The YouTube post alludes to the Sandy Hook Elementary School massacre but said she had planned her attack "well in advance" of the shooting there. "I now literally have a plan of seriously hurting … killing … murdering people in my high school," part of the post reads. It continues: "I WORK at the high school as a student teacher basically … which is why no one can find out about me somewhat accidentally planning to blow up the school. (and yes … it would be super easy)." The girl's parents said she had been seen by a psychiatrist "and had recently been inquiring about where the guns were being kept in the house", a police statement said. "The father said he was alarmed by his daughter's comments, and took the additional safety precautions of placing trigger locks on each gun and safeguarding them in a gun safe." The father owns three handguns. Police let the father keep the weapons. The teenager faces charges of computer tampering and threatening and intimidating, the statement read.