PHOENIX (AP) -- Authorities say a teenager is in custody for allegedly threatening to injure other students at a high school in the Phoenix suburb of Anthem.
Maricopa County Sheriff's officials say Nicholas Harrington Goettl, 18, a Boulder Creek High School senior, was arrested Monday.
"He admitted to the threats," said Sheriff Joe Arpaio. "He said they were fake; a joke."
They say he's been booked into jail on suspicion of hoax.
The student allegedly went online and posted a Twitter message that said he planned to bring a gun to school and shoot other students as part of a senior prank.
The Tweet said, "For my senior prank I'm going to bring an AR15 to school and kill everyone."
During the course of the investigation, other Twitter postings examined included one which contained a yearbook photo of Goettl's with a quote underneath that read, "I bear witness that there is no god but God. I bear witness that Muhammad is the messenger of Allah."
There was also information posted on a Facebook page connected to Goettl that referenced seniors starting a "Riot" on Monday because some students are not allowed to walk for graduation due to getting into trouble for vandalizing the school.
Sheriff's officials say a posse member who aids Boulder Creek High on security issues obtained information that led to the arrest.
The teen was contacted at his father's house in Anthem and was interviewed by sheriff's detectives and allegedly admitted to posting the threat.
The student reportedly had some air soft pellet guns, but did not have access to actual firearms. "You can't take anything for granted," says Sheriff Arpaio. "The person is using Facebook, Twitter to get this type of information. You can't know if he would ever follow through with his threat or joke or whatever you want to call it."
The Associated Press contributed to this story