Authorities in northeast Iowa say they have arrested a man who prompted a multi-school lockdown after he sent an email to a teacher, threatening to “retaliate” over a sex education curriculum.

Bruce “Deano” Divers Jr. faces charges of harassment after he sent a message to a teacher expressing his concerns that his fourth-grade son had been taught about masturbation and nocturnal emissions, Decorah, Iowa, police said.

The Decorah Community School District shut down all schools Monday over what officials called a “credible threat” at Carrie Lee Elementary School, according to NBC affiliate KWWL.  “The manner in which the complaint was phrased caused the school district and the police department to be concerned,” police said in a statement.

Police said someone had become “angry” about a curriculum matter at the school and had sent a message that caused alarm.

On April 9th, 2016 the Decorah Police Department became aware of a subject who was angry about a curriculum matter at…

Posted by Decorah Police Department on Sunday, April 10, 2016

“After thorough discussion with the Decorah Police Police Department and the Winneshiek County Attorney, precautionary safety measures will be taken at all district buildings,” the school district said Sunday in a statement. “Every effort will be made to provide a safe and secure environment which will allow your son or daughter to have a formal day.”

Divers told KWWL that he sent the email to a teacher at the elementary school because he took issue with the sex-ed lesson. The message, which was read to The Washington Post by a schools official, said in part: “Decorah schools spiritually declared war against my house today.”

It added that “when I retaliate Monday morning,” a third-grade teacher — who teaches the boy’s sister — would not be caught in the crosshairs.

Schools superintendent Mike Haluska told The Post that Divers said he was “looking to prosecute” two teachers who spoke to the students. Divers said he was taking on the district “because they have already committed war crimes against my family,” according to Haluska.

Haluska told KWWL that the school curriculum is intended to teach children about human growth and puberty. “Interestingly enough,” he said, “we have paperwork available at the beginning of the school year for anyone who wishes to have their children exempted from any conversations that have to do with that type of subject matter.”

Decorah Community Schools serve about 1,700 students from early childhood through 12th grade, according to the district, which says it aims to create “an environment that is student-centered, where individual needs are addressed, and students are encouraged to take responsibility for their own learning.”

The superintendent said schools were running as usual on Tuesday, a day after the lockdown.

Decorah police are working with the district and the Winneshiek County Attorney’s Office on the investigation. Divers was still in police custody Tuesday, and his bail has not been set, police said.

“We’re just thankful that the incident is over,” Haluska said, “and that our young people are able to resume their regular educational schedules.”