TEXAS (NYTIMES) - He had been entrusted with their care when they were at their most vulnerable, but prosecutors say that William Davis secretly preyed upon recovering heart surgery patients at a Texas hospital where he worked as a nurse by injecting air into their arteries.

       Four patients whom Davis injected later died, their once-encouraging conditions rapidly deteriorating and confounding doctors, the authorities said. He had injected at least seven patients in all, they said.

       On Tuesday, a jury in Tyler, Texas, convicted Davis of capital murder in the deaths of the four men after deliberating for about an hour. The verdict was confirmed by Ms Kaylee Hahn, an administrator for the 114th District Court, who said that the sentencing phase of the trial would begin on Wednesday (Oct 20).

       Prosecutors were seeking the death penalty for Davis, 37, who had worked for Christus Mother Frances Hospital in Tyler at the time that the patients experienced complications after heart surgery in 2017 and 2018. He was fired about a month before his arrest in April 2018. Tyler is about 160km east of Dallas.

       During the trial, prosecutors presented a portrait of Davis as a sadistic caregiver who slipped into patients' rooms when no one was watching and "enjoyed" injecting air into their arterial lines that caused fatal brain damage.

       Doctors were at a loss to explain what could have gone wrong until, the authorities said, they saw CT scans that showed air in the patients' brains. During the trial, prosecutors played security camera footage showing Davis entering the room of one of the patients. Three minutes later, the patient's heart monitor alarm sounded. He later died.

       "It turns out a hospital is the perfect place for a serial killer to hide," Mr Jacob Putman, the district attorney for Smith County, said during the trial.

       The victims were: Mr Ronald Clark, 68; Mr Christopher Greenaway, 47; Mr Joseph Kalina, 58; and Mr John Lafferty, 74.

       The Smith County District Attorney's office declined to comment on Tuesday because of the ongoing sentencing proceedings in the trial, which began on Sept 28.

       Mr Phillip Hayes, a lawyer for Davis, who lives in Hallsville, Texas, did not immediately respond to a request for comment on Wednesday.

       During the trial, Mr Hayes contended that all of the patients who died had shown signs of suffering a watershed stroke, a type of stroke that occurs when vulnerable border zones of the brain supplied by the three main cerebral arteries do not receive enough blood. Calling Davis a scapegoat, Mr Hayes also said that the patients had underlying medical conditions before their deaths.

       "I don't know if there's any evidence to show that it was foul play," Mr Hayes said during the trial.

       A spokesman for Christus Mother Frances Hospital said in an e-mail statement on Wednesday that protecting patients' health and well-being continued to be a top priority, in addition to "extending the healing ministry of Jesus Christ".

       "The jury's decision brings with it a range of emotions for our associates and - most especially - the people and families harmed by Will Davis," the spokesman said.

       "We pray for our community and all involved, and hope that the jury's verdict helps bring some closure to those harmed."

       Davis remains in custody at the Smith County Jail on US$8.75 million (S$11.7 million) bond.

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