Derek Mahlum was born and raised in Wolf Point, Montana. He started his career with the Wolf Point Police Department in 2004. During the time he worked with various state, local, tribal and federal agencies policing Indian Country.
In 2005, he took a position with the Havre Police Department where he worked until 2011. During this time, he served as a firearms instructor, field training officer and eventually promoted to the position of patrol sergeant. While working for the Havre Police Department, he enjoyed seeking out the most difficult of cases in order to develop them to be presented to the appropriate state or federal attorney for prosecution.
In 2011, he took a position with the Great Falls Police Department. He was later assigned as a general case detective in 2015 where he remained until 2020. During this time he led and assisted with numerous homicide/death investigations as well as various property crimes. In 2020, he was assigned to the newly created Cascade County Violent Crime Task Force. While in this position he was tasked with investigating violent felonies to include robberies, shooting, drug and gun trafficking crimes. In 2021, he was promoted to the position of sergeant and returned to patrol before being reassigned as the General Case Detective Sergeant.
Sgt. Mahlum is a member of the International Association of Identification and is also certified by the IAI as a Crime Scene Analyst. Sgt. Mahlum is the Montana Regional President for the Pacific Northwest IAI. Sgt. Mahlum is currently pursuing certification as a subject matter expert of cellular analysis.