Key takeaways from the fourth week of the Elizabeth Holmes trial.

SAN JOSE, Calif. — The fourth week of the fraud trial of Theranos founder Elizabeth Holmes lacked star power, but jurors got their most detailed look yet at how medical tests from the failed blood-testing start-up were plagued with inaccuracies.

In the trial’s first few weeks, several high-profile witnesses testified in the government’s case against Ms. Holmes, who had founded Theranos and built it into a $9 billion company before it spectacularly imploded. (She now faces 12 counts of wire fraud and conspiracy to commit wire fraud.) The star witnesses included Erika Cheung, a former Theranos employee turned whistle-blower, and former Defense Secretary James Mattis, who once sat on Theranos’s board.

But this week, jurors mainly heard intricate technical accounts of the problems with Theranos’s blood tests. Just two witnesses, both scientists, testified as prosecutors sought to show that Ms. Holmes had intentionally misled investors and others on her start-up’s track record.

Here are three takeaways from the week.

A Theranos lab director emerged as key for the prosecution.

Dr. Adam Rosendorff, who joined Theranos as a lab director in April 2013 before leaving the company in 2014, began his testimony last week and was still going on Friday. His four days on the stand so far have been the longest of any witness in the trial. He will resume on Tuesday.

His testimony stood out because of his senior position in Theranos’s lab. While previous witnesses, including Ms. Cheung, also testified to Theranos’s failed tests, Dr. Rosendorff provided greater detail about the range of problems — including how one test was so inaccurate it had “lost any diagnostic value” — and patient complaints.

He also had access to Ms. Holmes and said she had been aware of his concerns but pressed forward with Theranos’s commercial launch anyway.

In his testimony, Dr. Rosendorff said he became increasingly uncomfortable with the failure rate of Theranos’s blood-testing machines and the volume of physician complaints about inaccurate test results before ultimately quitting.

“The company was more about P.R. and fund-raising than patient care,” he said.

John Carreyrou, who exposed Theranos’s problems in 2015 while he was at The Wall Street Journal, revealed on Tuesday that Dr. Rosendorff was his “first and most important source” in breaking the story.

“Hats off to his courage and integrity,” Mr. Carreyrou wrote on Twitter.

Prosecutors emphasized that Theranos’s tests did not work.

The prosecution’s strategy this week centered on hammering home how Theranos’s machines routinely failed quality control tests and delivered inaccurate results.

One email presented during Dr. Rosendorff’s testimony described a patient who hadn’t felt “right” since increasing her dose of blood thinner medication in response to an erroneous Theranos test result.

Prosecutors walked another witness, Dr. Victoria Sung, who worked as a senior scientist at the pharmaceutical company Celgene while it was under contract with Theranos, through a Celgene slide show. It contained an analysis of Theranos’s tests that showed more unusable results and greater fluctuations than from commercially available alternatives.

Ultimately, Celgene cut its Theranos deal short.

The defense tried pinning the blame for Theranos’s testing problems on the lab director.

Lance Wade, Ms. Holmes’s attorney, spent three days this week grilling Dr. Rosendorff to establish that it was the lab director — and not his client — who was legally responsible for what had happened in Theranos’s lab.

Mr. Wade emphasized Dr. Rosendorff’s advanced science credentials, as compared to Ms. Holmes, who dropped out of Stanford University during her sophomore year. Dr. Rosendorff conceded that Ms. Holmes never instructed him to report an inaccurate result.

But according to emails and testimony introduced by the government, Dr. Rosendorff had raised concerns about inaccurate tests and quality control failures to Ms. Holmes and other top executives. Other email chains showed Dr. Rosendorff was left out of the loop on some patient complaints and testing decisions.

On Friday, Mr. Wade tried poking holes in Dr. Rosendorff’s credibility, pointing out times he was slow to respond to doctors’ complaints. Mr. Wade also showed the jury emails between Dr. Rosendorff, Ms. Holmes and former Theranos chief operating officer Sunny Balwani to show that they had been receptive to Dr. Rosendorff’s concerns.