The family of a murder victim in Durham Region's oldest cold case supports a controversial Mr. Big tactic used to extract a suspect's confession — even if a judge ruled it inadmissible.

"It took a lot of courage to go to the courtroom that day, knowing the outcome and knowing that our closure was going to be snatched from our hands," Barb Brown, victim Beverly Smith's twin sister, told CBC News.

Alan Dale Smith was acquitted of first-degree murder last month after a judge said his confession in the 1974 shooting death of Beverly Smith, no relation, could not be used as evidence during his trial.

"I’m actually glad that the ordeal is over with," Alan Dale Smith said after the acquittal.

Police first arrested and charged him with second-degree murder in the case in March 2008. A Crown prosecutor dropped the case because she said there was no reasonable prospect of a conviction.

Beverly Smith

Beverly Smith was 22 when she was shot to death at her home in Raglan, just north of Oshawa, in 1974. (Submitted)

Police later set up what is known as a Mr. Big sting and staged a murder to extract Alan Dale Smith's confession. But earlier this summer, the Crown withdrew its case after the judge's ruling that the confession was coerced. 

In a Mr. Big sting, undercover police officers lure a suspect into a fictitious criminal organization. To move up in the ranks, the target must eventually confess about a past crime to the organization's imaginary leader. 

Brown believes the confession was real and not coerced. She supports the police's undercover operation.

"I just I wonder how far they would expect the police to go if it was their mother or sister or daughter," she said.

Beverly Smith's daughter, Rebecca, was 10 months old and in the next room when her mother was killed.

"I'm always going to wonder what it would be like, you know, even to have siblings," said Rebecca. "I don’t know what it’s like to have a mother."

The slain mother was "a good person" who "shouldn't have died," said her twin sister Brown. "She was worth the Mr. Big to get the confession."

Shortly after Alan Dale Smith was acquitted, the Supreme Court of Canada ruled on a separate case involving a Mr. Big sting to extract a confession from Nelson Hart. That ruling clarified the laws around such operations, creating new standards for judges to consider.

With files from Sue Sgambati