A statement of defence filed recently in Court of Queen's Bench says the office acted in good faith and followed accepted procedures in investigating and prosecuting Unger.
The attorney general also says Unger was convicted largely on repeated confessions he made to undercover police officers in a sting operation.
Unger, who is now 43, was found guilty of first-degree murder in the 1990 death of Brigitte Grenier (GREHN'-yay) at a rock concert south of Winnipeg.
His lawsuit alleges he was tricked into making a false confession by undercover officers posing as gangsters who offered him money and work if he had committed a serious crime.
In 2009, the federal justice minister determined that the conviction had probably been a miscarriage of justice.
The provincial attorney general said the undercover sting, known as Operation Drifter in the Unger case, was accepted practice at the time.
"The investigation into Grenier's death, including all aspects of Operation Drifter, was conducted on a good-faith basis and in a careful and conscientious manner consistent with accepted law enforcement standards and procedures in place at the material time," the statement of defence reads.
"Any loss or damages ... were caused, or significantly contributed to, by the plaintiff's own conduct which includes but is not limited to his repeated confessions to having murdered Grenier."
The federal government used similar wording in its statement of defence filed last year. It also pointed out that while federal agents such as the RCMP were part of the investigation, the ensuing prosecution was the responsibility of the provincial Crown.
Unger was sentenced to life in prison along with his co-accused, Timothy Houlahan, but as the years went by the evidence used to convict him began to unravel.
An RCMP hair analysis expert had testified at Unger's trial that a hair found on Grenier's sweater belonged to Unger. It was the only physical evidence against him, but DNA tests in 2005 showed the hair belonged to someone else.
The only witness who claimed to have seen Unger kill Grenier was Houlahan, who committed suicide in 1994 while waiting for a retrial he was granted when he appealed his conviction. Unger's attempts to appeal were rejected.
The other key piece of evidence — the confessions Unger gave to undercover police officers — also came into question. Unger told them he had killed Grenier, but got several facts wrong. He mentioned a bridge at the concert site that had actually been built several months after Grenier's death.
Eventually, Unger was formally acquitted.
His lawsuit alleges that police and Crown attorneys relied on faulty science, ignored evidence that pointed to Houlahan as the killer and used a flawed undercover sting to get a false confession.
"The plaintiff was led to believe that if he said he committed the Grenier murder, he would receive a career, money, respect, companionship and many things sorely lacking in his life,'' Unger's statement of claim reads.
No court date has been set to hear the lawsuit.