Andy Rubin, chief architect and former head of Android, took to the stand at the U.S. District Court in San Francisco this week to once again undergo questioning about a cache of internal emails he exchanged about the creation of the Google (GOOG) mobile operating system.

The common thread tying together Rubin’s missives, which date back as far as 2005, is his team’s use of the Java programming language, which is owned by Oracle, to build Android. Oracle (ORCL) gained ownership of Java after its 2010 acquisition of Sun Microsystems. Java is free to use by third parties via application programming interfaces, or APIs, that connect disparate pieces of software. The companies are in court over what kind of use constitutes a violation of Oracle’s licensing agreements.

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Many of these emails are already familiar to followers of the intellectual property case, which has carried on for several years. The emails had been submitted for evidence for a weeks-long showdown between the Silicon Valley giants at the same federal courthouse in San Francisco in spring 2012.

On the third day of the retrial this week, one email in particular garnered attention. The note suggested that Rubin and his then-Google colleagues might have been more aware than previously known about how their use of Java could infringe upon its licensing agreement.

During cross-examination that lasted for approximately four hours, Oracle attorney Annette Hurst pressed Rubin about several of his emails, notably the following exchange, as described by Ars Technica:

In another e-mail exchange, Rubin was asked about another company’s plan to use Java.

“Wish them luck,” Rubin wrote. “Java.lang.apis are copyrighted. and sun [sic] gets to say who they license the tck to,” Rubin wrote.

Google began incorporating features from Java into Android in 2007, the same year the mobile operating system was first unveiled publicly. (At the time, Java was owned by Sun.) After acquiring Sun in 2010, Oracle requested that Google pay licensing fees. When the two couldn’t come to terms, Oracle sued Google for using its APIs without permission.

Oracle argues that Google stole its intellectual property, costing it billions of dollars in opportunity in the mobile market. Google argues that its implementation of Java APIs fall under U.S. copyright laws for fair use, which permits limited use of copyrighted material without licensing for creative, educational, and other purposes.

For more, read:
A Guide to Oracle v. Google, a $9.3 Billion Fair Use Fight

All throughout the legal battle—the 2012 trial, a subsequent stop at the Federal Circuit of Appeals, a petition to be heard by the U.S. Supreme Court (which was ultimately rejected), and now this week’s retrial—Rubin and other Google executives (including Eric Schmidt, executive chairman of Alphabet, Google’s parent company) have repeatedly defended Google’s use of the Java APIs, further insisting they believed they were free to use elements of Java without a license.

But this particular exchange involving Rubin, which has not drawn attention before, would seemingly undercut Google’s argument that it didn’t think it needed a license to use Java for building Android.

For more, watch:

Oracle is seeking more than $9 billion in damages from Google if it wins this go-around. However, even if the 10-person jury sides with Oracle at the end of this trial, it will likely again go to the appeals court, and possibly make another bid to be heard by the Supreme Court.