The US Federal Bureau of Investigation (FBI) is conducting a criminal investigation against Sepp Blatter, the suspended president of soccer's governing body, over his "full knowledge” of FIFA’s illegal activities.
FBI has called on Swiss authorities to aid the bureau on a probe into soccer corruption.
Blatter allegedly knew about $100 million paid as bribes to former members of FIFA.
It is alleged that FIFA officials, including ex-FIFA president Joao Havelange and former FIFA executive Ricardo Teixeira, received bribes from sports marketing company ISL.
The company, in return for its payments, gained television and marketing rights from the FIFA officials during the 1990s.
Havelange had to resign as honorary FIFA president over the scandal and Blatter is currently suspended by FIFA over a similar scandal.
Blatter, however, has denied any knowledge of the payments.
Meanwhile, media sources claim a letter written by Havelange reveals that Blatter had "full knowledge of all activities" in regards to the ISL payments and was "always apprised" of them.
It is not yet known in what year the alleged letter was written.
Media reports link FIFA's leadership with corruption, bribery, and alleged vote-rigging in the election of Blatter and the organization's decision to award the 2018 and 2022 World Cups to Russia and Qatar, respectively.
These allegations have led to the indictments of nine high-ranking FIFA officials and five corporate executives by the US on charges ranging from racketeering to wire fraud, and money laundering.
On May 27, 2015 several of these officials were arrested by Swiss authorities, who were launching a simultaneous but separate criminal investigation on FIFA.