HILTON, N.Y. (AP) — A Rochester, New York-area elementary school principal was charged with sexually abusing nine students during school in a case that prosecutors say goes back at least four years.

Kirk Ashton, the longtime principal of Northwood Elementary School in Hilton, was arraigned Wednesday night on multiple counts of first-degree sexual abuse, second-degree course of sexual conduct and endangering the welfare of a child.

The victims, all boys, were between 8 and 12 years old, prosecutors said at a news conference Thursday.

Ashton pleaded not guilty in Greece Town Court, and bail was set at $500,000 cash or $1 million bond.

“This predator preyed on these little boys,” Police Chief Andrew Forsythe said. “This guy who is charged with protecting, guiding and mentoring these children used their innocence and trust to violate them. Making matters worse, he chose one of our most sacred institutions, our schools, to carry out these disgusting acts.”

Monroe County District Attorney Sandra Doorley declined to detail Ashton’s alleged actions but said he is accused of engaging in sexual conduct multiple times with victims during the school day up until March 26, when state police were alerted following a call to the state Child Abuse Hotline.

The current charges date to 2017.

A sexual abuse educational program presented by the Bivona Child Advocacy Center just before the reports likely led alleged victims to come forward, state police Major Barry Chase said. The investigation began over spring break so Ashton never returned to school.

Authorities urged other potential victims to come forward.

“Have a conversation with your child. There could be more victims out there,“ Doorley said.

Assistant District Attorney Sara VanStrydonck said in requesting bail that Ashton was considered a flight risk. Defense attorney Robert King disputed that assertion.

King said Ashton hired an attorney after speaking with state police about 10 days ago. Ashton then went on vacation to Boston last weekend and returned to the area, the attorney said.

“If he wanted to make a run, the last 10 days was the time to do it,” King said.

VanStrydonck said that was before Ashton was made aware of the scope of the investigation.

Ashton, who had been at the school since 2004, was placed on administrative leave from the school district April 8.

“The School District has been cooperating fully with the State Police,” Hilton schools said in a statement. “Our primary concern is for our students.”

VanStrydonck said the investigation is “ongoing and extremely active.”

“Any time there are allegations of kids being hurt it’s upsetting to the community and it should be,” VanStrydonck said. “It’s upsetting as a parent. I think the community is hurting right now, as they should be, and hopefully at the end of this when we release some information, at least some lessons can be learned.”

Forsythe praised the victims for speaking up.

“These courageous little men, in the face of fear and uncertainty, showed their bravery and came forward to tell their story,” he said.

“We drop our children off to this guy every day. Myself, members of this police department, members of this community. We drop our children off to him. … All of us parents get them out there, get them on the bus, we drop them off,” the chief, growing emotional, said. “They’re going to be safe. They’re going to be protected. And this guy? The worst ever.”