Lars – also known as Colin – helped Phuket police out with many high profile cases, including when Norwegian Stein Dokset was charged with murder.
Wal Brown, the head co-ordinator of the Region 8 International Volunteers group, said Lars had arrived in Phuket before the 2004 tsunami.
He worked independently out of Chalong police station, and until recently, out of Karon police station. He regularly assisted the Tourist Police and the Thai Police with cases, due to his "impeccable" Thai language skills, Mr Brown said.
Mr Brown often came across him when dealing with cases, and would regularly see Lars around Phuket, often helping out at an accident scene or helping Thai Police direct traffic.
He even adapted his own vehicle to help with rescues, including writing "Rescue" on the side and fitting a siren.
"He took duty of care to heart," Mr Brown said.
"He was great with everyone. He was one of nature's gentlemen. He was one of those people who took volunteering the right way – he was such a nice guy. He will be missed by a lot of people."