Dave began his career as a prosecutor in the Denver District Attorney’s office. He then went to the US Attorney’s Office in Denver where he was the Coordinator for the Mountain States Drug Task Force as part of the Organized Crime Drug Enforcement Task Force newly formed in 1982.

In 1985, Dave was appointed by then Governor Lamm as the District Attorney for the First Judicial District of Colorado that includes Jefferson and Gilpin Counties. He was elected in 1993 and remained as the elected DA until 2005 when he was term limited.

In 1987, Dave was appointed by Governor Romer to be the Executive Director of the Colorado Department of Public Safety. He held that position until he was elected District Attorney in 1993. During his tenure, he attended the Harvard University Executive Course for Senior Government Executives.

Dave was the Executive Director of the District Attorney’s Council for three years in 2005. During that period, he was appointed by the Chief Judge for the Fifth Judicial District to be the Acting District Attorney in the Fifth Judicial District that includes Huerfano and Las Animas Counties.

Dave joined Defense Attorneys Maureen O’Brien and Fred Bibik in 2008 where he practiced criminal defense until 2022. Dave joined with his daughter, Attorney Carrie Kollar, in October 2022 to January 2024. Dave’s background includes litigating sex crimes, DUIs, drugs, murder cases, crimes against children, felonies, traffic and financial crimes.