PHOENIX -- Authorities say a 16-year-old girl from Mesa was arrested Thursday after she posted a threat on YouTube that she had a plan to kill people at her high school and then commit suicide.
The girl told deputies she planned to "cut the wires to security carts" to slow down response and was planning to shoot people from behind a fence.
The Maricopa County Sheriff Office says the girl had access to guns at her home, but never brought firearms to Red Mountain High School in Mesa.
Sheriff Joe Arpaio found eerie and what he referred to as "bizarre parallels" to the Connecticut massacre.
"The possible mental problems as cited by the parents, same number of weapons as in Connecticut, a high school, the access this 16-year-old had, the premeditation. It's awful," Arpaio said.
Deputies found a semi-automatic .40 caliber handgun, a .357 revolver and a .22 revolver in the house. The guns had trigger locks and were kept in a gun safe. They were not seized.
The agency says investigators arrested the girl at her home Thursday morning and that she admitted to posting the threat.
The girl's parents said their daughter had mental issues and was being seen by a psychiatrist.
Arpaio said this was not an attempt at a copy-cat crime, as the unnamed teen planned the attack approximately a week before the deadly shooting at Sandy Hook Elementary.
"We're going to continue to get all the details of what was in her mind and other facts regarding the circumstances that came to our attention," Arpaio said.
Red Mountain High School was in session Thursday. The school said it plans to have additional security on campus Friday, the final day of the semester.
Investigators in Arizona say they received a tip about the girl from Canadian police.
The girl was booked on charges of computer tampering and threatening and intimidating.
KTAR's Newsroom and KTAR's Sandra Haros contributed to this report.