William George Davis.Photo: Smith County Jail/AP/Shutterstock

William George Davis

William George Davis was a well-liked nurse in the halls of Christus Trinity Mother Frances Hospital in Tyler, Texas. Affable and friendly, he worked for five years with no major disciplinary marks on his record.

And then, in 2017 and 2018, everything changed.

Several patients began to suffer massive stroke-like symptoms as they recovered from cardiac surgery. While many of them survived the strokes with permanent damage, four patients died.

At first, they seemed like unfortunate coincidences. But as the hospital began to investigate, they noticed a disturbing pattern. Police said in Davis' 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.

As it turned out, Davis was injecting air into their IV lines, causing catastrophic neurological damage. His alleged motive was even more macabre: He told his wife that he was injuring the patients in an attempt to garner more overtime hours.

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

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Christopher Greenaway; Joseph Frank Kalina; Jay Clark

In October, Davis was convicted of four counts of murder. He has been sentenced to death.

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Davis' murderous spree has baffled the friends and families of the victims — but also stunned those who used to work with him.

“He didn’t need the overtime,” a fellow nurse who worked alongside Davis tells PEOPLE in the latest issue. “We were very understaffed. There was overtime available for anyone who wanted. So it doesn’t make any sense. My take on Will is that he was just a sick guy who wanted to kill.”

Meanwhile, many loved ones are wondering why Davis singled out their relatives and friends for death.

“Why did he choose Chris?” asked a friend of victim Christopher Greenaway. “It’s taken a lot of getting used to, to realize that this was just an evil person who did what he wanted to do, for whatever his reasons were. Chris was a man who we were fortunate to have in our lives. He had a lot of life left to live.”

source: people.com