William George Davis, 37, was seen on surveillance footage going into the rooms of patients recovering from heart operations moments before their conditions abruptly worsened.

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William George Davis
William George Davis
| Credit: Smith County Jail/AP/Shutterstock

A former nurse at a Texas hospital was convicted Tuesday of capital murder for killing four patients by injecting air into their arterial lines while they were recovering from heart surgery, a Smith County court official confirms to PEOPLE.

William George Davis, 37, worked at Tyler's Christus Trinity Mother Frances Hospital until he was fired in 2018. Police said in his arrest affidavit that on several occasions, he was seen on surveillance footage going into the rooms of patients recovering from heart operations moments before their conditions abruptly worsened.

Davis killed four people when the air he injected into their arterial lines in 2017 and 2018 caused brain damage: John Lafferty, Ronald Clark, Christopher Greenaway and Joseph Kalina.

Dr. William Turner, a cardiac surgeon at the hospital who treated Greenaway, Kalina and Lafferty, testified that air got into Greenaway's brain through the arterial line — a thin, flexible tube that is placed into an artery that allows medical professionals to check blood pressure and take samples. He testified that it was "inconceivable" that air got into Greenway's brain during surgery, the Tyler Morning Telegraph reports.

Dr. William Yarbrough, a pulmonologist, testified that brain scans showed that the patients' brain damage was caused by air. He ruled out blood pressure issues and any other causes of the damage other than injection of air, the Associated Press reports.

During opening statements of Davis' trial, Smith County District Jacob Putman said, "It turns out a hospital is the perfect place for a serial killer to hide."

PEOPLE's call to Putman's office was not immediately returned.

KLTV reports that before the jury's deliberations, prosecutor Chris Gatewood said Davis' motive was "simple: He likes to kill people. He enjoyed going into the rooms and injecting them with air. If you watch the video on Kalina, he set at the end of the hall and he watched those monitors and he waited. That's because he liked it."

PEOPLE's call to Davis' attorney, Phillip Hayes, was not immediately returned and it was unclear if Davis will appeal.

The AP reports Hayes said Davis was being scapegoated for problems at the hospital, and that he was merely at the wrong place at the wrong time. He said strokes occur often in intensive-care units, where Davis worked and where all four patients who died were treated.

Prosecutors plan to seek the death penalty during the sentencing phase of the trial, which began on Wednesday, the AP reports.

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This story originally appeared on people.com