A D.C. police lieutenant has pleaded guilty after being caught in a child sex abuse sting operation in Harford County, Maryland. Court records show Matthew Mahl, a 23-year veteran with the D.C. police department, was arrested in April after prosecutors said he traded sexually explicit messages with someone he believed was a 15-year-old boy. In addition to sexually explicit photos, Mahl sent a photo of himself in uniform. The operation was recorded as part of the Harford County Sheriff’s Office partnership with the “Takedown with Chris Hansen” series, which documents child predator sting investigations. Mahl pleaded guilty to two felony counts of solicitation of a minor on Aug. 7, in Harford County Circuit Court.