Maybe he wrote while in prison.
I was hoping to find the answer to that in the trivia section but nothing, so I came here. There was a lot of tallent involved with this film, Fiennes, Tucci, Hoskins. Those are the reasons I watched it.
Edmond dantes is an alias of John hughes who penned this movie.
sharei, too, was very interested in this. This is what i've found so far:
"Hughes wrote the script for the film "Beethoven," but used the name Edmond Dantes because so much of his work had come to the theater around that time and he was afraid there would be a backlash against him. The pseudonym is a homage to a character in The Count of Monte Cristo."
http://www.riverblue.com/hughes/trivia1.html
And wikipedia says that he's used that name for his recent movie "Drillbit Taylor".
I read somewhere that Hughes used the pseudonym to convey his feeling of havign been betrayed, in that he nearly lost the rights to the script. He had to fight a court battle to be credited for the story, but he was still not credited for the screenplay as the filmmakers edited his story so much.