Chuck Blazer went undercover to help the US government expose corruption in world football, according to details of his plea bargain made public on Monday night.
The 70-year-old former FIFA executive pleaded guilty to 10 charges, including bribery, money laundering and tax evasion, in 2013 - charges which carried a lengthy prison sentence.
However, he was given immunity from prosecution by agreeing to become an informant for the FBI and US justice department.
Blazer's 19-page plea agreement from November 25, 2013, was unsealed following a ruling by an American judge last week.
It reveals that Blazer, a FIFA executive committee member from 1997 to 2013, started providing information to the authorities in December, 2011.
The former general secretary of North American and Caribbean confederation CONCACAF admitted, among a series of revelations, that he and other FIFA officials took bribes in connection with the 1998 and 2010 World Cups.
