The trial entered its fourth day on Thursday, with Google engineer Timothy Lindholm taking the stand to answer questions about a 2010 email that has become a critical piece of evidence in the case.

Oracle sued Google in August 2010, saying Google's Android mobile operating system infringes its copyrights and patents for the Java programming language. Google countered that it does not violate Oracle's patents and that Oracle cannot copyright certain parts of Java, an "open-source," or publicly available, software language.

During opening statements, an Oracle attorney displayed several Google emails to the jury, calling them prime evidence that Google took its intellectual property.

One of them involved Lindholm, a former Sun Microsystems employee who began work at Google in 2005. Shortly before Oracle sued Google in 2010, Lindholm penned an email to Android chief Andy Rubin, saying he had been asked by top Google executives to investigate technical alternatives to Java for Android.

"We've been over a bunch of these, and think they all suck," Lindholm wrote. "We conclude that we need to negotiate a license for Java under the terms we need."

Oracle bought Sun Micro, the originator of Java, in 2010.

In court on Thursday, Lindholm acknowledged that he penned the email. However, he told Oracle attorney David Boies that he was not referring to a license from Sun.

"It was not specifically a license from anybody," Lindholm said.

Lindholm then told Google attorney Christa Anderson that he understood the software over which Oracle is claiming copyright to be free for use by other people.

Early in the case, estimates of potential damages against Google ran as high as $6.1 billion. But the company has narrowed Oracle's claims to only two patents from seven originally, reducing the possible award. Oracle is seeking roughly $1 billion in copyright damages.

The case in U.S. District Court, Northern District of California, is Oracle America, Inc v. Google Inc, 10-3561.

(Reporting By Dan Levine; Editing by Steve Orlofsky)

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