A former nurse was convicted on Tuesday of capital murder for killing four patients by injecting air into their arterial lines while they were recovering from heart surgery.

William George Davis, 37, worked at Tyler’s Christus Trinity Mother Frances Hospital in the Intensive Care Unit until he was fired in 2018. Between 2017 and 2018, he was responsible for the deaths of John Lafferty, Ronald Clark, Christopher Greenaway, and Joseph Kalina.

According to court documents, surveillance footage captured Davis going into the rooms of people who were recovering from heart surgeries just moments before their condition suddenly worsened.

Pulmonologist Dr. William Yarbrough testified that brain scans of the patients showed the damage was caused by injected air, and that he had ruled out blood pressure issues or any other cause.

Dr. William Turner, a cardiac surgeon at the hospital who treated three of the victims, testified that air got into Greenway’s brain through a thin tube placed into an artery, and that it was “inconceivable” that it happened during surgery.

During the opening statements of Davis’ trial, Smith County district attorney Jacob Putman said, “It turns out a hospital is the perfect place for a serial killer to hide.”

Davis’ attorney, Phillip Hayes, said that his client was simply in the wrong place at the wrong time, and is being blamed for strokes, which often happen in the ICU.

Before jury deliberations, prosecutor Chris Gatewood said Davis’ motive was “simple.”

“He likes to kill people,” said Gatewood. “He enjoyed going into the rooms and injecting them with air. If you watch the video on Kalina, he sat at the end of the hall and he watched those monitors and he waited. That’s because he liked it.”

No information has been released on whether or not Davis and Hayes will appeal. Prosecutors said they plan to seek the death penalty during sentencing.