Those methods of killing can leave few signs to show up in an autopsy.
"It's going to be very difficult," said Dr. Cyril Wecht, a nationally known forensic pathologist who serves as a county medical examiner in Pittsburgh.
He suggested that authorities should take their time and be "very selective" about which body to dig up.
"If you're going to nail this guy, and make sure he's not a kook or a nut or something, one case against him is as good as 50," Wecht said.
Efren Saldivar, a respiratory therapist, told police in suburban Glendale on March 11 that he committed the mercy killings of 40 to 50 terminally ill patients at Glendale Adventist Medical Center in the last decade. But police found no independent evidence to back up his claim and released him.
Although his state license was temporarily suspended and he was fired two days after his confession, no criminal charges were pending against him. By state and federal law, a confession alone isn't sufficient to bring a case.
Saldivar's whereabouts were unknown Sunday, although his brother said he was with relatives. He faced an administrative hearing Tuesday on whether his license should be permanently suspended.
Concerned family members of patients continued to flood police and the hospital with phone calls as criminal investigators tried to find corroborating evidence that would allow them to arrest and charge Saldivar.
A six-member task force has been combing through hospital records and interviewing staff and patient's relatives in a methodical investigation that police say could take months to complete.
No patient bodies have been exhumed yet but "that's a definite option as the investigation continues," police spokesman Rick Young said.
In his confession, Saldivar told police that he killed some gravely ill patients by giving them surgical drugs that can relax muscles to the point that the victim is unable to breathe.
The drugs, one called Pavulon and the other going by the initials SUCC, break down quickly in the body and may not leave a trace by the time the body is autopsied, Wecht said.
"They both are (nearly gone) in terms of minutes when they are given by injection," he said. "If the person lives for half an hour or an hour or two, it almost all is going to be metabolized."
Even signs of the drugs could prove only that the patients underwent surgeryÂ—not that they were killed. The drugs are given to help keep a patient still while the surgeon operates.
Saldivar's other admitted method of killing, decreasing the oxygen supply to patients on respirators, is tantamount to the perfect murder: it can't be determined at autopsy, Wecht said.
Adding t the difficulties facing investigators is the likelihood that most of the alleged victims were old and extremely ill with a variety of terminal diseases.
Written by Michael Fleeman.
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