US jurors heard clashing visions Thursday at fallen Silicon Valley star Elizabeth Holmes's trial, with prosecutors calling her a fraudster in closing arguments and the defense claiming she truly believed in her blood testing startup.

Holmes potentially faces years in prison if convicted on allegations she defrauded investors and clients of her once-hyped firm Theranos, which collapsed after it was revealed the machines did not work as promised.

The closing arguments in San Jose, California mark the nearing end of the high-profile case that has drawn intense media attention and posed questions about how far startups can bend the truth.

"Holmes chose fraud over business failure, she chose to be dishonest. That choice was not only callous, it was criminal," argued prosecutor Jeff Schenk, saying she knew the company would not deliver its grand vision.

Holmes launched Theranos in 2003 at age 19, eventually promising self-service testing machines that could run an analytical gamut cheaply and on just a few drops of blood -- a pledge shattered under fraud allegations.

'Recruit investors'

Holmes, who took the stand in her own defense in recent weeks, admitted to mistakes but argued she was deeply committed to Theranos and did not purposely mislead investors and patients.

"If someone is acting in good faith, you have no reason to find them guilty," defense attorney Kevin Downey told jurors.

"Miss Holmes believed that she had invented a very valid form of technology, she believed that others outside the company shared that view," he added later.

Downey is scheduled to complete his closing arguments on Friday, with jury deliberations to begin after the defense and prosecution have both concluded.

Holmes has also sought to put some of the blame on Ramesh "Sunny" Balwani, a boyfriend almost two decades her senior whom she brought in to help run the company.

Balwani, who is facing trial separately, has denied the abuse allegations that Holmes leveled against him during her testimony.

In his closing arguments, Schenk reminded the court of the testimony from former employees who had shared their doubts about the startup's machines, but also a pregnant woman who was told she was miscarrying based on faulty Theranos test results.

Schenk also noted how former Pentagon chief Jim Mattis recounted how he went from fascination to disappointment with Theranos when he was on its board of directors.

"Holmes's role was to recruit investors by making misstatements," Schenk alleged. "Holmes's role was to get money and keep Theranos alive."

As Theranos soared, it attracted luminaries such as Rupert Murdoch and Henry Kissinger, but a series of reports casting doubt on the firm's claims from Murdoch's own Wall Street Journal set the company's collapse in motion.

In many ways, Holmes fit the image of a Silicon Valley entrepreneur, from her dark-colored turtleneck sweaters that evoked tech legend Steve Jobs to her dropping out of California's elite Stanford University.

But the fundamental question has been whether she was a true visionary who simply failed, as she claimed on the stand, or a skilled self-promoter who took advantage of a credulous context to commit fraud.