A teenager arrested after a tip from a parent in Arizona and accused of threatening a mass shooting at his Las Vegas high school could face trial as adult on a felony terrorism charge, the top prosecutor in southern Nevada said Monday.

Clark County District Attorney Steve Wolfson didn't immediately respond to questions about specific plans to prosecute the 15-year-old, who was taken into custody Thursday on campus at Desert Oasis High School.

The boy's name was withheld because of his age, and it wasn't immediately clear if he had a lawyer representing him. He was being held in juvenile custody pending a court hearing on a charge of making a terrorist threat. A conviction as an adult on the felony charge carries a possible sentence of two to 20 years in state prison.

Clark County School District police Capt. Ken Young said the student wasn't armed when he was taken into custody Thursday at the high school.

Young declined to say whether weapons or a written threat were found in a search of the boy's home, or if he had other access to weapons. "At this point, we're not discussing any of the evidence," he said.

Young told reporters that investigators believe the boy acted alone, and the alleged threat wasn't connected with a recent rash of clown-themed rumors that have disrupted schedules at schools in Las Vegas and elsewhere.

"He made statements that were concerning about a possible shooting at the school, planned for the near future," Young said in an interview after a news conference.

Young said local, state and federal authorities were investigating — and school police decided to act even though the alleged threat didn't specify a certain time or date.

Parents in Las Vegas were notified by email afterward, he said.

Young credited a parent of a teen in Arizona with alerting authorities in Southern California and then Nevada about the alleged threat after overhearing a Skype conversation from a Desert Oasis student about rumors that another student planned an attack. The parent wasn't identified.

"This parent did some research and ... made a responsible call," Young said. "It's not unusual for us to investigate a rumor. In this particular case, the information turned out to be good."

"We may never know how important that particular parent was to this case," he said.