A teacher who worked with deaf and hearing-impaired students in three north metro school districts is under criminal investigation after a school technology staff member discovered thousands of photographs of elementary schoolchildren, some in compromising positions, on his computer, the Anoka County Sheriff’s Office said Tuesday.

The Spring Lake Park and St. Francis school districts were notifying parents Tuesday of the investigation. The teacher works for Northeast Metro 916 Intermediate School District and does contract work in St. Francis and Spring Lake Park.

The teacher has not been charged, and the investigation continues, the Sheriff’s Office said. The Star Tribune generally does not name suspects until they are charged. The teacher has no prior criminal history, according to authorities.

The teacher, who was first hired by District 916 in 1999, was placed on paid leave in May.

Troy Ferguson, St. Francis schools interim superintendent, said Tuesday that he launched a district investigation in May when the teacher was seen with two young students sitting on his lap.

Ferguson ordered the teacher’s computer searched. The St. Francis technology coordinator discovered about 3,000 photographs. Ferguson said that four of the pictures raised concerns and that the Sheriff’s Office was immediately contacted. He also said the parents of the six children — the two sitting on the teacher’s lap and the four in the photos — were immediately notified.

Forensic computer detectives reviewed thousands of photos on the computer, the Sheriff’s Office said Tuesday. Detectives are now interviewing children depicted in some of them. Some were students of the teacher and some were students in the school where the teacher worked.

It appears most of the photos were taken in schools, according to Cmdr. Paul Sommer. He declined to elaborate on the nature of the photos or the number of students.

“They meet the statutory definition of child pornography,” but the children were not aware they were being victimized, Sommer said.

“Every kid we have reached out to, interviewed and talked to, none of them has cognitive awareness they were victimized. None of them reported inappropriate touching,” Sommer said.

The teacher in question was initially arrested on suspicion of interference of privacy, but was later released without charges pending further investigation.

Once the investigation is completed, the case will be referred to the Anoka County attorney’s office.

Officials in the Spring Lake Park District could not immediately be reached for comment Tuesday. Connie Hayes, District 916 superintendent, said her district had not heard from any parents. She added: “Safety is deeply interwoven into all our district decisions and practices.”

District 916 is one of three intermediate school districts in Minnesota created to help share resources and costs for highly specialized programs. Part of District 916’s mission is to serve 400 children with disabilities from 10 north metro districts.