Oracle told a federal court in San Francisco that Google executives knew they should have paid it for a licence to use elements of the Java programming language in Android, the world's best-selling smartphone operating system.
Java is integral to Android and its apps, and at the centre of the court case. A decision in Oracle’s favour could cost Google billions of dollars, on an operating system it already gives away to smartphone manufacturers.
"You will see email after email in which Google executives knew this day would come," said Oracle lawyer Michael Jacobs.
The first stage of the case covered Oracle’s claim of copyright infringement of Java APIs, or Application Programming Interfaces, by Google. APIs are ready-made software components that make it much easier for apps to ‘talk’ to an operating system such as Android.
Oracle argued that Google’s use of the Java APIs without its permission was unlawful.
"If Google can just take the APIs and be forgiven under fair use, that licensing falls apart," said Mr Jacobs, referring to Google’s defence that it had a right to use the APIs under the “fair use” doctrine in US copyright law.
It allows use of copyright materials without permission in the public interest and is typically used to defend news reporting and academic work from legal attacks. Jacobs told the court that Google’s copying was “just copying - copying for a business purpose”.
In its closing argument, Google claimed it did not copy Oracle’s Java code, but created its own APIs.
“There was no copying here because Google knew that it couldn't use Sun's source code,” said the firm’s lawyer Robert Van Nest.
“This kind of use of APIs in this way where you use the minimum you need to be compatible is fair use,” he added.
Google also cited comments by Jonathan Schwartz, the former CEO of Sun Microsystems, which owned the rights to Java when Android emerged in 2007. He seemingly welcomed Google’s use of the APIs at the time, saying that he was “offering my heartfelt congratulations to Google on the announcement of their new Java/Linux phone platform, Android”.
"If that isn't an affirmative endorsement of a product, I don't know what is," Mr Van Nest said.
Oracle countered that “Google knows better than to claim a blog post is official permission”.
The first section of the case, which will move on to alleged patent infringement next week, is being closely particularly watched by intellectual property experts as a potential test of whether it is possible to copyright a programming language, which could have a massive impact on the software industry. Previously only programs, not programming languages, have been protected by copyright.