His death came hours after the publication of the Barron Report which named him as a prime suspect in the 1974 Dublin bombings.
Evidence from Wallace was used by the Barron Report, an Irish government inquiry into the Dublin and Monaghan bombings.
According to the Irish Government's Barron Report, he was also "reliably said to have had relationships with British Intelligence".
Retirement (Barron Report)
His 1999 sworn affidavit was published in the 2003 Barron Report on the Dublin and Monaghan bombings.
The Barron Report lists him as one of the suspects in the Dublin bombings.
The interviews revealed many similarities in the way the attacks were carried out, while various documents (including the Barron Report) established a chain of ballistic history linking weapons and killings to the gang.
The 2003 Barron Report suggests that the guns were taken from the stockpile of weapons at the Glenanne farm.
These allegations were published in the 2003 Barron Report, which was the findings of an official investigation of the bombings by Irish Supreme Court Justice Henry Barron.
The 2003 Barron Report, however, concluded that the Monaghan bombing was perpetrated solely by the Mid-Ulster Brigade.