A former Washington County sheriff's sergeant has admitted to having sex with a 15-year-old boy in Idaho after meeting him through a dating app in 2015.

Michael Alexander, 46, of Lake Oswego pleaded guilty Friday in Canyon County 3rd District Court in Idaho to lewd conduct with a child under 16. He is scheduled to be sentenced May 8.

An additional charge of enticing a child over the Internet was dropped as part of a plea agreement. The maximum penalty for the lewd conduct charge in Idaho is life in prison, said Joe Decker, a Canyon County spokesman.

Alexander, a patrol sergeant based in Cornelius, was placed on unpaid administrative leave in late February 2016 when the Meridian Police Department in Idaho told the Washington County Sheriff's Office that it was investigating text messages between Alexander and the boy, according to a search warrant affidavit.

The texts included discussions of the two having sex in Alexander's pickup and a photo of the sergeant wearing his uniform and badge while sitting behind a desk with a sheriff negotiator placard on it, the affidavit said.

Alexander resigned in March 2016. He had worked for the Sheriff's Office for 19 years. Alexander declined comment when reached by phone Thursday.

The boy told investigators he created an account on Grindr in January 2015 and claimed he was 18. He reported beginning to text with Alexander while on vacation on the Oregon coast two months later. Alexander drove to the boy's home in Idaho while his parents were away that June and sexually abused the child, the affidavit said.

The two had another sexual encounter in September when Alexander again drove to Idaho, picked up the boy from his home and had sex in his truck while parked at a business parking lot, the affidavit said. The two continued to text each other afterward.

The investigation began when the boy's mother discovered the texts between the boy and Alexander.

Alexander's arrest last year came amid criminal investigations that led to the firing or resignations of three Washington County sheriff's deputies.

Dan Cardinal, a former sergeant, was sentenced to two years of probation in January 2016 for repeatedly having sex with female co-workers while he was on duty. He pleaded no contest to official misconduct.

Former Deputy David Bergquist received a year and a half of probation that March for pulling a female colleague's breast out of her clothing and putting his mouth on it during a union party in 2015. He pleaded guilty to sexual harassment.

Former Cpl. Jon Christensen was sentenced in September 2016 to two years of probation for choking a female co-worker the year before while demanding that she continue with their sexual relationship. He pleaded guilty to coercion, strangulation and official misconduct.

The three all were placed on leave after an anonymous letter was sent to the Sheriff's Office and The Oregonian/OregonLive in April 2015 claiming widespread sexual misconduct by workers in the agency. Bergquist wasn't named in the letter, but the other two were.

Christensen was later fired by the Sheriff's Office. Cardinal and Bergquist resigned.

The female deputy who was attacked by Christensen has since sued him, the county, the sheriff and others alleging the agency regularly subjected her and other female employees to sexual misconduct by male colleagues, discouraged them from reporting it and retaliated against her for disclosing wrongdoing.

-- Everton Bailey Jr.

ebailey@oregonian.com

503-221-8343; @EvertonBailey