Rowling says she'd planned on writing a similar book herself, with the profits going to charity.
BBC News has a report on Vander Ark's turn in the witness box.
Update: In another high profile copyright case, BBC Worldwide has today seen off a challenge to its use of the Daleks in books, reports Paul Lewis for Media Guardian.
The Daleks, famous for their "exterminate!" catchphrase, were the creation of the late Terry Nation, who wrote the second Doctor Who serial, The Daleks.
Paul Fishman, the son of one of Nation's friends, had claimed at the high court in London that his company, JHP, held the book copyright to dalek stories and that a new publication about the characters by BBC Worldwide had infringed that copyright.
But a judge ruled today that although JHP held a licence to publish several books by Terry Nation about the daleks in the 1960s, it did not own the copyright.