I'm writing this in August 2002. I was reading an Economist article dated August the 1st, 2002, about the convinction of Tommy Suharto. The full article requires a subscription but the first paragraph is:
It was arguably Indonesia's trial of the century, and the verdict surprised many. The 15-year prison term handed down on Hutomo Mandala Putra, better known as Tommy Suharto, on July 26th for murder looked tough. It certainly would never have happened when Tommy was a spoiled young playboy and his father was president. But does this mean that the winds of change are at last blowing through the Indonesian legal system? Alas, not quite.
Forgive me for being pedantic, but it seems just a little early to be declaring anything the ‘trial of the century’, even within a single country.
In fact that's not the earliest example though; the Philippines have put their former president on trial, and this too is being described as the ‘trial of the century’:
Indeed, there was hope that the so-called ‘Trial of the Century’ would finally put an end to the cycle of impunity of those in public office. Yet today, with everything seemingly going wrong, the trial is instead turning out to be a showcase of the problems the Philippine court system has become notorious for, including sheer incompetence, politicking and the influence of personal relationships.
That article is dated January the 16th-18th 2002, and mentions April the 4th 2001 as the date that charges were filed. It doesn't state clearly who is calling it the trial of the century, unfortunately.
Are these people really so certain that nothing so interesting will happen in a court for another 90+ years? It's all a a bit life imitates onion, really.
2004-06-17: The BBC describes the trial of Marc Dutroux as Belgium's trial of the century. A media sensation, certainly, but there's still 95 years to go...
2004-12-13: The BBC reports that Saddam Hussein's trial, which hasn't (at the time of writing) even happened yet, ‘has already been described as “the trial of the century”’.
2005-02-04: The Economist reports, in the issue dated 5th of Feburary:
Jury selection began in the so-called “trial of the century”. Michael Jackson, a pop-star phenomenon, is accused of molesting children at his ranch; he says he is innocent.
To be fair, this time they don't say who is calling it that. In the full article on the subject the (much more fairly) describe it as ‘the highest profile paedophilia trial of all time’.
2009-09-21: The Telegraph describes the Clearstream trial as the “trial of the century”. Their justification may be the origins of the case at the top of France's political class:
“A duel of this kind, at this judicial level, has never been previously seen in the annals of French history, nor, as far as I know, abroad,” said Guy Carcassonne, a constitutional lawyer.
(Presumably he is referring only to civil cases rather than to criminal prosecutions though.)
2010-05-26: CNN reports:
About 600 witnesses are expected to testify in a trial that started Monday for a bank heist some call Argentina's "robbery of the century."
[...]
During the robbery, Telam said, robbers ordered pizza and soft drinks for the hostages, sang happy birthday to a female lawyer and left behind toy guns.
Again, unclear who is calling it that.
I should note that The Economist and the BBC are over-represented here because they are my main news sources, not because they are particularly prone to this turn of phrase.