Mark Pieth told The Associated Press that FIFA and its President Sepp Blatter cited legal reasons for "repeatedly" denying his requests to see the document.
"This is something that needs to be publicized. We asked FIFA to get it. We have repeatedly and right from the beginning asked," Pieth said, acknowledging that to release the document now risked a contempt of court charge.
Earlier Friday, Switzerland's Federal Tribunal announced it extended a block on publication requested by two unidentified parties.
The parties — widely reported to be Brazilian former football leaders Joao Havelange and Ricardo Teixeira — are appealing against five Swiss and British media organizations which have won lower court rulings to access the ISL dossier.
The document reveals details of a May 2010 deal in which two officials admitted taking kickbacks in the 1990s. They repaid 5.5 million Swiss francs (then $6.1 million) on condition their identities would remain secret.
"Nobody has really seen that document because it would be a contempt of court issue if they gave it to us," the University of Basel professor said. "He (Blatter) has not given it to anybody because he is not allowed to. That's the point."
Pieth said it was "crucial" for his 13-member expert panel to study the ISL case, as they examine how serious FIFA was about investigating scandals, including alleged bribery and vote-rigging, in recent years.
"This is another element for us to say, 'Look, we are not satisfied how these things have been dealt with.' But we want to see it officially and we want to see it published," the former United Nations investigator said.
Blatter asked Pieth in November to suggest widespread transparency and governance reforms of football's embattled world governing body that would take effect before June 2013.
Pieth's expert panel has sent an initial report that Blatter's executive committee will consider at a two-day meeting opening next Thursday in Zurich.
The ISL scandal has clouded Blatter's presidency since 2001, and seeking closure has become a central part of his promised mission to improve FIFA's image.
Still, FIFA is no longer formally involved in the appeals being considered by Switzerland's highest court.
On Friday, the federal court said it granted a "suspensive effect" to parties identified only as "B2" and "B3" who appealed to stop publication. FIFA was party "B1" but withdrew in December.
Swiss business weekly Handelszeitung and the BBC have reported that the parties are former FIFA President Havelange and his former son-in-law, Teixeira.
The five media parties, including Handelszeitung reporter Jean-Francois Tanda, want to establish if the football officials got preferential treatment under Swiss law, and if other FIFA staff were aware of the unethical payments.
The journalists won a ruling in December when a court in Zug canton said publication was in the public interest.
The federal court verdict is expected in several months, and Blatter has said he cannot fulfil a promise to publish the ISL document until that decision is handed down.
"I think the federal court should speed up a bit," Pieth suggested. "In politically sensitive issues they could work a bit faster."
As the legal saga continues, Teixeira resigned this month as head of Brazil's football federation and the 2014 World Cup organizing committee, and gave up his FIFA executive committee seat on Monday, citing unspecified health and personal reasons.
The 95-year-old Havelange, who remains FIFA's honorary president, is currently being treated in a Rio de Janeiro hospital for a bacterial infection.
He resigned his 48-year IOC membership citing health reasons in December, days before the Olympic body was due to sanction him following its own investigation into wrongdoing connected to ISL.
The ISL scandal stemmed from alleged payments of tens of millions of dollars to sports officials made by the Swiss-based marketing agency before its 2001 collapse with debts of $300 million.