The Senior Vice President of the Canadian Imperial Bank of Commerce, Denis Leyne was removed from his position in 1991 after he was investigated for his links to Sean John McCann, who had been charged with trying to purchase a Stinger missile for the Provisional Irish Republican Army. The following year, Leyne was arrested himself as part of a 1992 investigation that alleged that four citizens of the Republic of Ireland had conspired to ship detonators to the Provos. Due to a massive heart attack, he died less than a year after his acquittal.
In 1956, Denis immigrated to Canada and took a job as a banker. He married Maureen Moore, with whom he had four sons and a daughter .
Denis Leyne, Michael Quigley and Greth Dillon formed a group named "Action Grosse Ile", and published a book titled "The Holocaust at Grosse Ile".
Denis Leyne was arrested as he flew from Toronto to New York City in 1992. Although he was granted bail on November 17, he was held pending extradition to Arizona to face charges; amidst complaints from family members that visits were difficult. Canadian Security Intelligence Service (CSIS) agent Richard D. Garland testified against Leyne, although he was acquitted of all charges on April 26, 1994.
Despite being found Not Guilty, CSIS continued to watch Leyne, and agent Don Lunau sought Auxiliary Postal Inspector John Farrell's help in stealing a postal relay key, to allow them to intercept Leyne's mail without the required judicial warrant.
Denis Leyne died of a massive heart attack on February 5, 1995. A Gaelic Athletics Tournament, hosted by St.Michael's Gaelic Football and Hurling Club, in Toronto was named in his honour.