Blewitt was last seen on April 12, 2004, in Melton.

Investigators suspected foul play early on, connecting his disappearance with the 2003 murder of underworld figure Graham "The Munster" Kinniburgh.

Police charged Stephen John Asling with Kinniburgh's killing in November. Police have alleged Blewitt was part of the hit team that killed Kinniburgh, and that the slaying was ordered by drug kingpin Carl Williams as part of his war against the Moran crime family. 

Purana Taskforce detectives located what they believe are Blewitt's remains during a search of a property in Thomastown in Melbourne's north.

Police spokeswoman Kelly Grindley said in a statement detectives have been searching and digging at the Pelmet Crescent property since Monday morning, finding the remains late on Wednesday afternoon.

"While the human remains are yet to be formally identified, detectives believe they are that of missing man Terrence Blewitt," she said.

"The current owner of the property has no connection to the investigation."

Pelmet Crescent is in an industrial estate.

Ms Grindley said a search was generated by police intelligence and information received by the investigating members.

Detectives are also hoping the search will provide further evidence in relation to Kinniburgh's murder, she said.

Purana Detective Inspector Andrew Gustke, who is expected to speak with media on Thursday morning, said the investigation has been complex and protracted. 

"Purana Taskforce investigators have taken hundreds of statements and interviewed hundreds of people during these investigations," he said. 

"We owe it to the family and friends of any victim of crime to investigate and do our very best to bring out some justice for them, and that's what we are hoping to achieve with this discovery." 

Kinniburgh, 63, had parked his car and was walking to his two-storey house on December 13, 2003, when he was gunned down.

He was a lifelong friend of Judy Moran and her former husband Lewis.

Mick Gatto was a pallbearer at his funeral.

Kinniburgh was considered an influential standover man, who had convictions for dishonesty, bribery, possession of firearms, resisting arrest and assaulting police.

Kinniburgh was implicated by a coroner in 2002, along with Jason Moran, in the death of gangster Alphonse Gangitano in 1998.

Williams, bashed to death in Barwon Prison in 2010, always denied any connection to the Kinniburgh murder.

"My conscience is clear," Williams told The Age less than 48 hours after the killing.'

"I've never met him and I've never heard a bad thing said about him. I have nothing to profit from his death. It's a mystery to me."

In mid-2013, police seized a blue Hyundai Excel which had been linked to the slaying of Kinniburgh and Blewitt.

On the day the car was seized in Alexandra, a $100,000 reward for information regarding Kinniburgh's murder was announced.

Blewitt has not been seen since he was spotted walking towards a similar car on April 12, 2004, in Melton.

A similar car had  reportedly been seen leaving Belmont Avenue in Kew shortly after Kinniburgh was shot.

Anyone with information is urged to contact Crime Stoppers on 1800 333 000 or submit a confidential report at www.crimestoppersvic.com.au.