Moose was born in 1953 in New York City, New York. His family moved to Lexington, North Carolina, shortly after he was born, and Moose lived and attended school there until leaving for college. Moose completed his Bachelor of Arts degree in U.S. History in 1975 at the University of North Carolina at Chapel Hill. That year he joined the Portland Police Bureau in Portland, Oregon, as a patrol officer. He then earned a Master of Public Administration degree from Portland State University in 1984, and a Ph.D in urban studies and criminology in 1993.

In 1993, Moose became the police chief of the Portland police force and served as the top law enforcement official for the city until 1999. During his time in Portland he also taught at Portland State University and was a member of the Oregon Air National Guard. On August 2, 1999, he became the 15th Montgomery County, Maryland, Police Chief. In October 2002, he was the primary official in charge of the efforts to apprehend those responsible for the Beltway sniper attacks. On June 18, 2003, Moose resigned from the Montgomery County Police to write a book about the sniper attacks. In September 2003, Moose released the book about the investigation titled Three Weeks in October: The Manhunt for the Serial Sniper (ISBN 0-525-94777-9). He resigned because he was barred by contract and Montgomery County policy from accepting a monetary advance for the book while still performing his job.

Until 2005, Moose served as the Squadron Commander of the 113th Security Forces Squadron, D.C. Air National Guard, United States Air Force. While Moose served with that unit, he deployed to Operation Katrina and served as military liaison and adviser to the New Orleans Police Department in the wake of Hurricane Katrina. Moose was promoted to Lieutenant Colonel and served as a Security Forces Officer in Hawaii.

Moose has since graduated from the Honolulu Police Academy and reported for duty as one of the members of the Honolulu Police Department.