According to the Hollywood Reporter,
Aug 17, 2001
News
According to the Hollywood Reporter, Harry Potter screenwriter is already in negociations to pen a screenplay for Prisoner of Azkaban.
Kloves wizardry on 3rd ‘Potter’
August 16, 2001 – The Hollywood Reporter
Three months before releasing the first installment of its highly anticipated “Harry Potter” franchise, Warner Bros. is negotiating with the film’s screenwriter, Steven Kloves, to adapt the third installment of the blockbuster children’s book series. (Zorianna Kit)
(Thanks to Majandriah at the Harry Potter Connection)