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William Jansen arraignment

William Jansen enters his not guilty plea July 24 in Twin Falls County Court.

TWIN FALLS — Fourteen jurists heard the state’s case Wednesday against a former Twin Falls police officer accused of sexually abusing young girls.

Former patrol officer William Anthon Jansen of Twin Falls was charged April 10 and put on unpaid leave. In July, Jansen pleaded not guilty to four counts of lewd conduct with a minor. Jansen is no longer with the department.

Lt. Terry Thueson Thueson told Judge John Butler during Wednesday’s testimony that Jansen’s former neighbor Detective Rick VanVooren brought rumors of the alleged abuse to the department before Jansen was hired in December 2013. As part of a routine background check, Thueson interviewed one of the alleged victims, who then denied the abuse.

Jansen was a sergeant in the Idaho Army National Guard and completed two combat deployments to Iraq.

A teenage girl came forward with the allegations in late March last year, saying Jansen sexually abused her in 2008 and 2009 when she was between 7 and 9 years old. She told a sheriff’s detective that Jansen also abused at least two other girls — one who has since died and another who said Jansen abused her in 2005 and 2006 when she was 8 years old. Jansen is accused of touching the then-preteen girls’ genitals with his hands when he was in his early 20s.

“As soon as we found out about the allegations, we forwarded to the sheriff’s office for investigation,” Twin Falls spokesman Joshua Palmer told the Times-News. “Then they conducted their investigation.”

A sheriff’s investigator said he believes “many more” victims will be uncovered.

“Based on my training and experience and the evidence gathered in this investigation, I believe more victims will be uncovered through the course of this investigation and Jansen remains a threat to society and any current/future victims,” Detective Travis DeBie wrote in a sworn affidavit. “It took these victims many years to come forward. I believe we will uncover many more.”

The girls testified in court Tuesday, followed Wednesday by Jansen’s ex-wives, Nicole Mathis and Amanda Barnes. Mathis and Barnes both testified that Jansen had confessed during their marriages to abusing young girls.

Mathis earlier told sheriff’s investigators Jansen admitted to “inappropriately touching juvenile girls” and to having sex with a 17-year-old roommate that lived with them while they were married. She also told investigators that Jansen was sent home dishonorably from his Mormon mission “due to a sexual incident that occurred” prior to the mission.

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She told detectives Jansen disclosed to his Mormon bishop that “he had inappropriate contact with juveniles.”

Jansen told detectives he was never alone with the girls he’s accused of abusing, one of whom said Jansen showed her a book depicting sexual acts the first time he assaulted her. He admitted to having sex with the roommate but said he believed she was 18 years old.

Ada County deputy prosecutors Kassandra Slaven and Abby Kostecka rested their case against Jansen Wednesday afternoon.

Attorneys Joe Filicetti and Scott Pearson of Boise will begin their defense at 9 a.m. Thursday.


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