Chuck Blazer, the corrupt Fifa official who pleaded guilty to charges of bribery, money laundering and tax evasion, has been working undercover for US investigators since 2011.

The 70-year-old was a member of Fifa’s executive committee for 18 months while he was cooperating with authorities. The American was on Fifa’s executive committee from 1997-2013.

Blazer struck a deal with prosecutors, details of which have been revealed after a judge agreed to a request by five media groups.

The US justice department last month announced charges against a total of 18 people for alleged involvement in football-related corruption. Blazer and three others have pleaded guilty, while seven FIFA officials arrested in Switzerland on May 27 are fighting extradition to the USA.

The 19-page co-operation agreement was signed in November 2013 – the day Blazer pleaded guilty – but references written agreements between himself and the US government dating back to 29 December 2011.

The plea agreement says: “The defendant agrees to furnish to the office all documents and other material that may be relevant to this investigation… and to participate in undercover activities pursuant to the specific instructions of law enforcement agents.”

Blazer has admitted taking bribes to vote for South Africa to host the 2010 World Cup, and implicated former FIFA vice-president and head of Concacaf Jack Warner

According to Blazer the pair took bribes from Morocco for its 1998 World Cup bid and from South Africa for 2010. Warner has always denied any wrongdoing.

Blazer, who is seriously ill with cancer, has already forfeited 1.95million US dollars as part of his agreement with authorities.

The New York Daily News reported last year that Blazer had recorded meetings with fellow Fifa executives at the London 2012 Olympics with a wire device concealed in a key fob.