JOHANNESBURG — A soccer referee named Ibrahim Chaibou walked into a bank in a small South African city carrying a bag filled with as much as $100,000 in $100 bills, according to another referee traveling with him. The deposit was so large that a bank employee gave Mr. Chaibou a gift of commemorative coins bearing the likeness of Nelson Mandela.

Later that night in May 2010, Mr. Chaibou refereed an exhibition match between South Africa and Guatemala in preparation for the World Cup, the world’s most popular sporting event. Even to the casual fan, his calls were suspicious — he called two penalties for hand balls even though the ball went nowhere near the players’ hands.

Mr. Chaibou, a native of Niger, had been chosen to work the match by a company based in Singapore that was a front for a notorious match-rigging syndicate, according to an internal, confidential report by FIFA, soccer’s world governing body.

FIFA’s investigative report and related documents, which were obtained by The New York Times and have not been publicly released, raise serious questions about the vulnerability of the World Cup to match fixing. The tournament opens June 12 in Brazil.

The report found that the match-rigging syndicate and its referees infiltrated the upper reaches of global soccer in order to fix exhibition matches and exploit them for betting purposes. It provides extensive details of the clever and brazen ways that fixers apparently manipulated “at least five matches and possibly more” in South Africa ahead of the last World Cup. As many as 15 matches were targets, including a game between the United States and Australia, according to interviews and emails printed in the FIFA report.

Although corruption has vexed soccer for years, the South Africa case gives an unusually detailed look at the ease with which professional gamblers can fix matches, as well as the governing body’s severe problems in policing itself and its member federations. The report, at 44 pages, includes an account of Mr. Chaibou’s trip to the bank, as well as many other scenes describing how matches were apparently rigged.

After one match, the syndicate even made a death threat against the official who tried to stop the fix, investigators found.

“Were the listed matches fixed?” the report said. “On the balance of probabilities, yes!”

The Times investigated the South African match-fixing scandal by interviewing dozens of soccer officials, referees, gamblers, investigators and experts in South Africa, Malaysia, England, Finland and Singapore. The Times also reviewed hundreds of pages of interview transcripts, emails, referee rosters and other confidential FIFA documents.

FIFA, which is expected to collect about $4 billion in revenue for this four-year World Cup cycle for broadcast fees, sponsorship deals and ticket sales, has relative autonomy at its headquarters in Zurich. But The Times found problems that could now shadow this month’s World Cup.

■ FIFA’s investigators concluded that the fixers had probably been aided by South African soccer offici