Chief Mullin comes to the Lawrenceville Police Department with 25 years of public service experience. He started his law enforcement career in 1997 after graduating from the John Jay College of Criminal Justice with a bachelor's degree in criminal justice and a minor in forensic psychology. He worked for the Fulton County Police Department until 2006 when he joined the Sandy Springs Police Department as one of its original 86 officers. He was promoted to the rank of Sergeant in 2007 where he worked in the Criminal Investigation and Uniform Patrol Divisions, and also served as the department's internal affairs investigator. He went on to serve as Captain in multiple roles, including Criminal Investigations, Special Operations, and District Patrol Commander. Chief Mullin served as Major over both administration and the day-to-day operations of the department as it grew to over 180 employees. Chief Mullin joined Forsyth County in 2021 as Director of Code Enforcement, Animal Control, and the Park Rangers Division, serving a growing county of over 250,000 residents.

Chief Mullin has a master's degree in public administration from Columbus State University. He is a graduate of the Southern Police Institute at the University of Louisville and a graduate of the Senior Management Institute for Police. He is also a graduate of the FBI Law Enforcement Executive Development Seminar. Chief Mullin was also a part of the 25th Delegation to Israel with the Georgia International Law Enforcement Exchange (GILEE) through Georgia State University. He is a graduate of the Georgia Chiefs Executive Officer Training Class as well as a member of the Georgia Association of Chiefs of Police and the International Association of Chiefs of Police.