TORONTO -- The fate of an Ottawa professor facing extradition to France over suspicions he was involved in a synagogue bombing there hinges on a "wholly unreliable" analysis of five words, Ontario's highest court heard Monday.

French authorities suspect Hassan Diab, 59, was involved in the anti-Semitic bombing of a Paris synagogue in 1980 that killed four people and injured dozens of others. Diab denies any role in the deadly attack, saying the unwavering moral principle throughout his life has been to promote equality and respect for all.

Lawyers for Diab challenged the decision to extradite him Monday in the Court of Appeal for Ontario, arguing before the panel of three judges that fundamental mistakes were made.

"(The charter) requires that the court not be a rubber stamp," lawyer Marlys Edwardh told the judges. "A jury could never reasonably convict," based on this evidence, she said.

Diab was committed for extradition in 2011 to face French authorities, even though Ontario Superior Court Judge Robert Maranger acknowledged the case against him was weak. He had to surrender himself into custody for the duration of the appeal hearing, expected to last two days, but about two dozen supporters attended court Monday.

The case centres on whether a handwriting analysis that linked Diab to the bombing is reliable, Edwardh said. French expert Anne Bisotti looked at writing on a hotel registration card believed to have been written by the bomber. It includes the suspected fake name of Alexander Panadriyu and the words Lanarca, technician and Cyprus in block letters.

Bisotti concluded there was a "very strong presumption" Diab wrote it, but the defence found three other experts who cast doubt on Bisotti's report.

The three defence experts said they were "deeply troubled" by how Bisotti reached her conclusions and criticized her "glaring failure to use recognized methodology," Edwardh said.

"Her conclusions are wholly unreliable," Edwardh said. "Justice Maranger fundamentally misappreciated the evidence before him."

Appeal Court Justice Robert Blair challenged Edwardh on whether she could establish that the Bisotti report was unreliable.

"You're just asking us to accept (the defence experts') opinion over her opinion," he said. "Just because you pile up five experts against France's expert, doesn't mean you win."

The court should keep in mind Canada's history with wrongful convictions when weighing expert evidence, Edwardh said, citing the cases of disgraced pathologist Charles Smith. Once considered an unassailable expert on child forensic pathology, an inquiry found that errors in Smith's work were responsible, in part, for several people being wrongfully convicted and sent to prison for killing children.

In April last year, then-justice minister Rob Nicholson signed an extradition order surrendering Diab to France.

The RCMP arrested Diab, a Canadian of Lebanese descent, in November 2008 in response to a request by France.

Diab's lawyers are arguing that Nicholson made several mistakes, including opting to surrender him even though France has not yet decided whether to put him on trial for the bombing.

The federal government argues that Maranger correctly ruled he could not refuse to commit Diab simply because the evidence against him is weak.

Federal lawyers also say Diab is the subject of a French arrest warrant and "there is no requirement" that authorities must also have made a decision to refer his case to trial.

Diab's lawyers have also expressed concerns that France is relying on secret intelligence in its case, which would leave Dib unable to defend himself should he eventually stand trial. In his brief, Diab argues it is plausible the intelligence France will rely on was derived from torture.

That issue attracted the attention of a number of groups who have intervened in the case -- Amnesty International, the Canadian Civil Liberties Association and the British Columbia Civil Liberties Association.

The Appeal Court judges are set to hear arguments from the Crown on Tuesday.