Evidence against Apple consists of a string of emails and phone calls between Eddy Cue, Apple senior vice-president of internet software and services, and representatives of the five publishers, excerpts of which have been published in a series of slides on the DoJ website.
She said: "The plaintiffs have shown that the publisher defendants conspired with each other to eliminate retail price competition in order to raise ebook prices, and that Apple played a central role in facilitating and executing that conspiracy.
"Without Apple’s orchestration of this conspiracy, it would not have succeeded." She added that a further trial would be held to determine damages.
However, Apple insisted on its innocence and said it was planning an appeal.
In a statement, the company said: "Apple did not conspire to fix ebook pricing and we will continue to fight against these false accusations.
"When we introduced the iBookstore in 2010, we gave customers more choice, injecting much needed innovation and competition into the market, breaking Amazon’s monopolistic grip on the publishing industry. We’ve done nothing wrong and we will appeal the judge’s decision."
Assistant attorney general Bill Baer, said: "As the department’s litigation team established at trial, Apple executives hoped to ensure that its ebook business would be free from retail price competition, causing consumers throughout the country to pay higher prices for many ebooks."