KENTVILLE, N.S. -- The prosecution service in Nova Scotia withdrew a first-degree murder charge Wednesday in the case of a missing woman because of concerns evidence gained through an undercover police sting may no longer be admissible.

Crown attorney Robert Morrison says Albert Baird was released from custody after a hearing in Kentville provincial court. The case was in court for a status update before a preliminary inquiry, which was set to begin early next year.

Baird was arrested and charged in May 2013 following the 2002 disappearance of his common-law partner, Rhonda Wilson, a 31-year-old mother of three.

Morrison said he withdrew the charge because of a Supreme Court of Canada decision on so-called Mr. Big police sting operations.

The high court noted several problems with the Mr. Big strategy in its July 31 ruling overturning the conviction of Nelson Hart in the deaths of his young daughters in Newfoundland in 2002.

Morrison said he had concerns that evidence gained through an undercover operation in the Baird case would no longer be admissible, diminishing the prospect of conviction.

"We looked at all the other evidence we had and it just didn't add up to a realistic prospect of conviction," he said in an interview.

He said the technique was used in the Baird case, but he couldn't provide any other details.

Baird's defence lawyer Brian Callender confirmed the investigative technique was used.

He said the Hart decision was the key to Baird's defence.

"Basically the tables were turned. ... The defence was placed in a position of strength with the release of the Hart decision," he said.

In 2010, the Nova Scotia government offered a $150,000 reward for information leading to a conviction in the case as part of its Major Unsolved Crimes Program. At the time, police received a number of possible sightings of Wilson, but none that was substantiated.

Morrison said he informed Wilson's family before the charge was withdrawn, adding that some of her relatives were in court for Wednesday's proceedings.

"For us it was a difficult decision, but it is one that had to be made," he said. "For the family, they were looking for something to happen and I think they were disappointed."

Callender, who is based in Kingston, Ont., said the Supreme Court of Canada decision has helped protect the rights of the accused.

"I think the Supreme Court of Canada got it right. I don't think it would have been a fundamentally fair prosecution based on how the evidence was obtained," he said.

In its judgment, the Supreme Court said prosecutors must prove a Mr. Big confession is admissible by showing it's reliable, and that it won't unfairly prejudice a crime suspect during court proceedings. The Crown must also prove the evidence was not obtained via police coercion, or was facilitated due to a suspect's mental health or addiction issues.

The Mr. Big investigative technique involves undercover police officers who recruit a suspect to a fictitious criminal organization while posing as gangsters.