SAN FRANCISCO — Former Theranos lab director Adam Rosendorff took the stand in the trial of Elizabeth Holmes for his third day Wednesday, facing an extended and often tense cross-examination from defense lawyers.

Defense attorney Lance Wade questioned Rosendorff about his responsibilities as lab director, pointing out that he was responsible for many things, including readying the lab for inspections.

Rosendorff shot back, suggesting that it wasn’t reasonable to pin everything on him.

“You keep saying ‘it’s my job, it’s my job,’ but I was part of a large company with delegated roles,” Rosendorff said. “Yes, I did my job, but I also depended on a lot of people around me.”

Holmes, the founder and former chief executive of Theranos, is on trial in federal court in San Jose, accused of misleading investors and patients about the company’s portable blood-testing device. Government prosecutors allege Holmes knew that the machine was not working as advertised and that Theranos was relying heavily on outside lab machines while telling investors otherwise. Holmes’s attorneys have said the founder made mistakes but acted honorably and did not commit fraud.

Holmes has pleaded not guilty.

Rosendorff’s testimony could be detrimental to Holmes’s defense. Her attorneys have sought to suggest to jurors that Holmes acted in good faith and that others below her might have known of issues that she did not.

Rosendorff confirmed on the stand Tuesday that he talked to a Wall Street Journal reporter about his time at the company and expressed concerns that Theranos’s technology was not ready for its public launch.

“I felt obligated to alert the public,” Rosendorff said during his testimony, according to Bloomberg News.

Theranos collapsed in 2018, three years after a Journal investigation raised significant issues regarding the company’s workforce and operations. The reporter, John Carreyrou, went on to write a book about the company.

In the book, he refers to a former employee by a pseudonym, “Alan Beam.” In reality, that is Rosendorff, he confirmed Tuesday.

“Adam was my first and most important source,” Carreyrou tweeted Tuesday. “Without him, I wouldn’t have been able to break the Theranos story. Hats off to his courage and integrity.”

Rosendorff first took the stand Friday, after former U.S. defense secretary Jim Mattis testified earlier in the week. Defense lawyers began questioning Rosendorff on Tuesday and will continue questioning him on Friday.

Rosendorff and Wade often sparred during questioning, occasionally talking over each other. More than once, Wade said he did not “have a question pending” when Rosendorff tried to expand on his answers.

Wade showed emails including concerns Rosendorff had raised with quality-control tests.

It was Rosendorff’s job to raise those issues, Wade said, adding “that’s why you get paid the big bucks.”

“Not as big bucks as you get paid,” Rosendorff responded to the defense lawyer, eliciting a laugh from the jury and audience.

Wade said that Rosendorff, who made about $240,000 a year at the company, was among Theranos’s highest-paid employees.

Rosendorff cut in, saying he should have been paid “much more” given the issues at the company. Wade asked the judge to strike the comment from the record, and Judge Edward J. Davila agreed.

Under Wade’s questioning, Rosendorff confirmed that he signed off on validation reports for blood tests on Theranos’s device, called the Edison. Wade asked Rosendorff to confirm he would not have signed off on the reports if he found the device “inherently unreliable.”

Rosendorff agreed.

Rosendorff will take the stand again Friday. In the meantime, the government called a new witness to the stand. Victoria Sung worked at pharmaceutical company Celgene in 2009 when the company held meetings with Theranos about possibly using its technology.