William George Davis

William George Davis stands Sept. 28 during opening day of his capital murder trial. The former nurse’s charges are connected to the deaths of four patients at Christus Trinity Mother Frances Louis and Peaches Owen Heart Hospital in Tyler (Michael Cavazos/News-Journal Photo)

After 11 days of testimony and presenting evidence, the prosecution will officially rest its case Wednesday morning in the capital murder trial of a former East Texas nurse accused of killing four patients at a Tyler hospital.

William George Davis, 37, of Hallsville, is accused of injecting air into patients’ arterial systems while he was a nurse at Christus Trinity Mother Frances Louis and Peaches Owen Heart Hospital in Tyler, causing their deaths, according to 2018 and 2021 indictments.

Davis is accused of killing John Lafferty, Ronald Clark, Christopher Greenaway and Joseph Kalina. His trial began Sept. 28.

The jury heard from the state’s remaining witnesses for nearly five hours on Tuesday before ending just after 1 p.m. The defense’s attorneys will begin calling witnesses Wednesday after the prosecution has officially rested.

Dr. William Yarbrough, a pulmonologist and professor of internal medicine in the Dallas area, testified Tuesday about his opinions on the case and provided expert testimony from his 40 years in the medical field.

He said the arterial system moves blood away from the heart, and explained to the jury the process of blood flow to the brain, blood pressure and typical strokes.

Yarbrough reviewed the brain scan images of Greenaway, Kalina, Clark and Lafferty as well as a patient Davis is accused of harming in 2017, Pamela Henderson.

Yarbrough testified there were significant defects at the surface of the brains, which is the working part of the organ. He said the air found inside their brains was always at the surface.

For each patient, Yarbrough testified that air injected into the arterial system of the brain was the cause of brain injury and death. While looking at Greenaway’s brain scan, he said the arterial line would be the most likely way of air coming into the arterial system.

On different dates in 2017 and 2018, the patients had unexplained neurological events while having otherwise routine recoveries from their heart surgeries. Air was found in each of the brain scans taken after the complications.

Yarbrough said he ruled out blood pressure issues or any other cause besides the injection of air. He also testified these events had to happen after the surgeries because the complications occurred after they began to recover.

While answering questions from the defense, Yarbrough said the bulk of his work is spent representing hospitals in medical malpractice suits.

Yarbrough said he was able to determine if the patients’ brains had air, not another form of gas, by viewing the brain scan images. He testified he’d never seen air in the arterial system of the brain before being a part of this case.

The defense noted Yarbrough’s previous reports called air in the arterial system a probable cause of the patients’ deaths, but his report just before the trial said the air in the brain was the definitive cause.

Yarbrough said Christus Trinity Mother Frances and the district attorney’s office didn’t ask him to make a certain opinion on the patients’ medical records.

Dr. Kennith Layton, a radiologist who specializes in diagnostic radiology and neuroradiology out of Dallas, returned to testify Tuesday morning for questions from the defense.

Layton said hypotension can commonly cause a stroke in patients but he didn’t see a hypotensive state that was significant enough to cause the stroke events in the patients Davis is accused of killing or harming.

The brain is able to accommodate periods of low or high blood pressure, Layton said, noting that hypotension would have to be very profound for five to 10 minutes to cause brain damage.

The defense noted Layton wrote down air and/or a toxic substance being injected as the reason for the gas in the brain and damages in his reports.

“I think it was air but I can’t exclude the fact that another substance could’ve been injected,” Layton said.

He testified he can definitely tell that the substance in the patients’ brains was gas.

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