FLORENCE, Ariz. (AP) -- A prosecutor announced an indictment Thursday against an 18-year-old Arizona student charged with sexually assaulting about a dozen girls over nearly five years.
Charges against Tyler Kost of San Tan Valley include multiple counts of sexual assault with a minor, sexual abuse with a minor and sexual conduct with a minor. He also faces one count of child molestation.
Pinal County Attorney Lando Voyles said the victims in the crimes alleged in the indictment issued Wednesday ranged from 12 to 17 years old.
Voyles said the offenses occurred between October 2009 and April 2014.
Kost was born in January 1996 so he was 13 when the first offense allegedly occurred. But Voyles plans to try him as an adult on all charges.
"In Arizona, once an individual turns 18, we don't have a choice," Voyles said. "(State law) makes it fairly clear."
Attorneys with the law firm representing Kost did not immediately respond to requests for comment.
During a hearing last week, an attorney for Kost requested a change of venue and a gag order on the Sheriff's Office. The judge said he could not address those requests and told the defense to bring up the issues again once Kost is formally charged. Kost is scheduled to be arraigned May 16.
Kost would face between 147 and nearly 334 years in prison if convicted of all the charges in the indictment, the prosecutor said.
Pinal County sheriff's deputies arrested Kost last week, accusing him of being a serial sex predator who assaulted at least 18 students. Voyles said he could not comment on why the indictment accused Kost of crimes involving only 11 victims.
According to the indictment, none of the alleged sexual assaults occurred on a school campus. Kost is accused of sexually abusing the victims in his bedroom, in a parked car, a park and out in the desert.
During a news conference, Voyles encouraged parents of sexual assault victims to report the crimes to authorities.
"Let your children know that we start by believing," he said.
In addition to calling Kost a sexual predator, Pinal County Sheriff Paul Babeu last week said Kost threatened and harassed victims to such an extent that two fled the state, and one attempted suicide.
"This is a serious and serial sex offender and rapist," Babeu said.
The investigation was initiated after the Sheriff's Office received a call March 25 from someone reporting that Kost had sexually abused and molested five teenage girls.
Kost lives in San Tan Valley, a bedroom community of about 87,000 named for its location in the foothills of the San Tan Mountains. The area, about 45 miles southeast of Phoenix, is known for its golf courses and hiking trails.
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