Defence lawyers made the claim during the trial of four men accused of murdering Lynda Spence at the High Court in Glasgow.
Ms Spence, 27, has not been seen since leaving her parents' home in April 2011.
David Parker, 37, from West Kilbride, Paul Smith, 47, from Largs, Philip Wade, 42, from Glengarnock, all North Ayrshire, and Colin Coats, 42, from Glasgow, are on trial accused of abducting, torturing and murdering her. They deny all the charges against them.
Defence QCs Gary Allan, who is representing Wade, and Derek Ogg QC, representing Coats, suggested that Ms Spence had been recruited by the Scottish Crime and Drug Enforcement Agency (SCDEA) as an "informer", to pass on information about a man named Sokal Zefaj, who they claim is part of an Albanian organised crime gang.
Ms Spence, who also went under the aliases Lynda Zefaj, Linda Riley, Lynda Palmer and Lynda De-bono, was said to have been married to Mr Zefaj before her disappearance and the lawyers pointed to this as a possible reason for her being recruited by the SCDEA.
While questioning Crown witness detective sergeant Aileen Boyle, who interviewed Coats for almost five and a half hours when he was detained on October 31 2011 in relation to Ms Spence's abduction and murder, during which he made no comment, Mr Allan asked if she had been made aware of such a claim.
Ms Boyle said she had not.
She said no SCDEA officers were present at a briefing on May 13 2011, when Ms Spence's missing person inquiry became a "major investigation" after the case was deemed to be "high risk".
Mr Allan said: "We may hear that far from being an ordinary businesswoman, she (Ms Spence) was in fact up to her neck in criminal activity."
Ms Boyle replied: "I would agree she was involved in criminal activity."
The lawyer went on: "Were you ever made aware that Ms Spence was recruited by the SCDEA to be a grass on the inside of an organised criminal network?"
Ms Boyle: "I did not know that."
Mr Allan asked: "So you did not have that angle on your inquiry at all?," to which she replied: "That's not information that would be shared."
Mr Allan went on to ask about the hierarchy of the investigation, to which Ms Boyle responded by saying that she was "low down", despite having interviewed one of the suspects and leading a search of a property in West Kilbride, Ayrshire, where prosecutors believe Ms Spence was held hostage and murdered.
Ms Boyle was also cross-examined by Mr Ogg, who told her Ms Spence had been recruited by the SCDEA not to provide information about any of the four men in the dock, but about Mr Zefaj, who he described as being involved in an organised crime gang.
He said Ms Spence was married to Mr Zefaj, and it was "for this reason that she was recruited by the SCDEA and a UK agency, the Serious Organised Crime Agency".
Mr Ogg asked Ms Boyle: "If this had been known, would it have placed Ms Spence's life in danger?"
Ms Boyle relied: "If that were the case, there would be serious concern for her safety."
The lawyer also claimed that a woman who Ms Spence was living with at the time of her disappearance contacted the missing woman's SCDEA "handler" with concerns about her safety two days after she vanished.
Ms Boyle again said she had no information on this.
Parker, Smith, Wade and Coats are alleged to have forced Ms Spence into a car on April 14, 2011 and held her hostage in a West Kilbride flat for up to a fortnight, where they are said to have blindfolded her and cut off her thumb.
The men are accused of crushing the woman's toes, burning her hands, severing her finger and hitting her with a hammer and a golf club, in an apparent bid to extract financial information from her.
Prosecutors say the men cut off Ms Spence's head and attempted to cover up their crimes by bleaching floors, pulling up carpets and laying new floorboards.
The four accused have pleaded not guilty to the charges.
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