Apple and Qualcomm continued feuding over alleged witness tampering, as the iPhone maker reiterated Tuesday it had reason to suspect its key witness had been influenced ahead of his testimony at a patent infringement trial in San Diego.

In a filling on Tuesday, Apple counsel Juanita Brooks wrote that the iPhone maker had grounds to suspect someone was trying to sway Arjuna Siva's testimony, though she said the company doesn't know who. The iPhone maker has argued that Siva, a former Apple engineer, co-invented technology in one of three disputed Qualcomm patents and should be named on it.

"Apple had good reason to be concerned that steps were being taken to influence Mr. Siva's testimony," Brooks wrote in the filing.

When Apple first made the allegation last week, Qualcomm said it was "ridiculous" and vigorously denied the claim. Judge Dana Sabraw, who is presiding over the case, also said there was "no evidence" for the allegation.

Siva, who now works at Google, testified on Monday after Apple said last week he was no longer intending on appearing in court. He said many elements of a boot-up technology covered by the patent were "my idea," but stopped short of claiming he was an inventor.  

The controversy over Siva's appearance has been a source of drama in what is an otherwise highly technical patent case. Qualcomm alleges Apple infringed on its patents in the development of some versions of the iPhone. One of those patents allows a smartphone to quickly connect to the internet once the device is booted up.

Apple alleged witness tampering last week when Siva seemingly backed out of his appearance after retaining new counsel. The new lawyer, Matt Warren, advised Siva against attending if he hadn't been subpoenaed. Apple suggested foul play because Warren was formerly a partner at Quinn Emanuel, the firm currently representing Qualcomm.

Last week, Apple filed subpoenas for both Siva and Warren to appear in San Diego. Warren, Siva's new counsel, had also retained an attorney of his own.

On Monday, Warren's counsel wrote in a letter filed to the court that the witness tampering claims were "baseless." In the letter, Warren's counsel said that Google, Siva's current employer, had arranged for Warren to be Siva's independent counsel. He said Google had only learned of Siva's expected testimony last Wednesday, and that asking for a subpoena was a "routine request."

In the court filing, Brooks said Apple's defense had worked with Siva for months before "things changed." Still, she said Siva's testimony had been consistent with the original plans, so she saw no reason for "further action" regarding Siva's testimony.

The San Diego patent trial is only the part of a long-running legal saga between Apple and Qualcomm. The two companies will meet in court again in April to argue over royalties for technology in iPhones.