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Apple said Thursday that its star witness in a patent trial against Qualcomm doesn't intend to appear in court anymore, a striking twist in the long-running legal battle between the two tech giants.

The companies are fighting over three patents that Qualcomm says Apple infringed in the development of some versions of its iPhone. One of those patents allows a smartphone to quickly connect to the internet once the device is booted up.

Now playing: Watch this: Apple vs. Qualcomm: Court battles explained

Apple has argued that one of its then-engineers, Arjuna Siva, co-invented the technology and should be named on the patent as well.

Siva was scheduled to testify later in the trial, but Apple counsel Juanita Brooks said Thursday that won't happen. She said Siva has retained new counsel that has advised him not to answer Apple's questions. He isn't intending to appear, but if subpoenaed, he'll testify, Brooks said. Siva, who now works for Google, was expected to arrive in San Diego on Wednesday night but never boarded his flight, she said.

Apple can still play Siva's video deposition.

The loss of a star witness is a blow to Apple's prospects for the trial, which is just the latest in a wide-ranging legal saga. Two years ago, the Federal Trade Commission, aided by heavyweights including Apple and Intel, accused Qualcomm of operating a monopoly in modem chips. The agency argued that Qualcomm's high royalty rates stopped competitors from entering the market, driving up the cost of phones and hurting consumers. That trial took place in January, and the parties are waiting for a decision.

The San Diego trial, presided over by US District Judge Dana Sabraw, is more technical than the other parts of the legal battle. But it could have implications for how your phone is made and how much it costs. Aside from the boot-up patent, the companies are fighting over two others. One of them deals with graphics processing and battery life. The third lets apps on your phone download data more easily by directing traffic between the apps processor and the modem.

Brooks said Siva's new counsel is a former partner at Quinn Emanuel, the law firm representing Qualcomm. She accused Qualcomm's defense of witness tampering, and indicated Apple wouldn't be subpoenaing Siva. "He's a tainted witness," she said.

Qualcomm's counsel, David Nelson of Quinn Emanuel, vigorously denied the accusation, getting animated as he addressed Sabraw. "I don't get angry very often," he said. "I lead this team. I consider this a personal attack."

"We wanted Mr. Siva to testify," Nelson said, adding that he and his team were enjoying putting together the cross-examination for the witness.

Sabraw said the court would continue to look into the matter. "It's a serious allegation," he told Nelson. "There's no indication that you or anyone at Qualcomm has had anything to do with this."

Later Thursday, after the jury had been dismissed for the day, both lawyers addressed the issue with Sabraw again. Nelson argued that Apple should've subpoenaed Siva in the first place to ensure his attendance.

Brooks countered that Apple had no reason to subpoena him because he was Apple's client and had cooperated up until now, including with pretrial meetings. She reiterated the claim of witness tampering. "Someone got to him. We don't know who got to him," she said. "Who has the motivation to shut up Arjuna Siva? I don't know."

Sabraw said Apple can decide to subpoena Siva for a separate hearing without a jury to get to the bottom of what happened.

Nelson and Brooks declined to give additional comment.

'A complex set of things'

Meanwhile on Thursday, Qualcomm and Apple continued their arguments in court. Because two of the patents in question concern improvements in battery life, Qualcomm asked Apple employees about the importance of power-saving.

Phil Schiller, Apple's chief of worldwide marketing, said in a video deposition that consumers factor in "a complex set of things" when they decide to buy a phone. "People care about battery life, but not in isolation," he said.

Schiller also stressed the importance of Apple's brand when it comes to consumers' purchasing decisions -- not just the device's capabilities. He said sometimes people want to buy an Apple product just because it comes from Apple. "There are lots of things people think about," he said. "Some are features and some are not features."

Qualcomm also showed a video deposition from James Imahiro, an Apple market research manager, who discussed the results of a recent iPhone buyer survey. Customers cited battery life on the survey, but in a slide about important aspects in purchasing an iPhone, respondents in the also US most frequently answered, "It was time to replace my old phone."

Originally published March 7, 9:34 a.m. PT.

Update, 10:22 a.m. PT: Added more information from the trial, and 5:08 p.m. PT: Added more details.