Suicide pacts are rare - they constitute half of one percent of suicides nationwide. Even rarer are charges filed against a person who survives, experts say.
In a hearing scheduled for Friday, Yiambilis' attorney will try to persuade a judge to dismiss the murder charge before the case goes to trial. Citing the Pennsylvania criminal code, attorney William Goldman said a person cannot be charged with criminal homicide for causing someone's suicide unless it was done by force or deception.
"I can't state emphatically enough that this was not murder," Goldman said. "His mom left notes to donate her hair to Locks of Love. She said she was taking Gus home to God."
Goldman said Karen and Gus Yiambilis were both unemployed; he had lost his job at a bank and she at a camp. Each suffered from various health problems. He had an anxiety disorder and past brain trauma, and she had fibromyalgia, a disorder associated with widespread pain. They had loads of medical debt and were facing eviction.
"She was tired of being cold and hungry, and Gus felt like a total failure. He was a broken man," Goldman said. "They turned to each other. They consoled each other."
Bucks County Deputy District Attorney Alan J. Garabedian declined to comment. In a recent court filing, he wrote that there was enough evidence to bring the homicide charge to trial. That evidence includes the high level of carbon monoxide in the apartment. Gus Yiambilis also told police he was the one who ran the generator, even refilling it after it ran out of gasoline, Garabedian wrote.
The prosecutor also cited Gus Yiambilis' statement to police at the hospital where he was being treated for carbon monoxide poisoning in which he said, "I can't believe I killed my mother. She's the only thing I got."
At this stage in the legal process, prosecutors need only to argue that a crime likely occurred and that a defendant is likely to have committed it. In late May, a Bensalem district judge reviewed the charges at a preliminary hearing and ruled the case strong enough for trial.
Donna Cohen, a professor at the University of South Florida who has studied suicides and homicide-suicides, said "incomplete suicide pacts" were rare. When charges are filed, courts often consider whether the survivor manipulated or deceived the person who died, she said.
Court decisions vary, she added. For example, an Ohio man was found not guilty of negligent homicide in 1995 after he and his girlfriend formed a suicide pact. She was supposed to shoot him and then herself. But after he gave her the gun, she shot only herself. But in California in 2010, an appeals court upheld a man's murder conviction after he made a suicide pact with his wife. Both planned to strangle themselves with ties around their necks, but he helped to pull hers around her neck and was thus guilty, the court ruled.
Yiambilis' case will be far from clear-cut if it reaches trial in its current form, said James A. Shellenberger, a Temple Law School professor. He said the prosecution had taken something of a "kitchen-sink approach" in charging the son with both aiding suicide and criminal homicide.
"Either she commits suicide or he killed her," Shellenberger said. "It can't be both."
Amos Goodall, a lawyer in State College, Pa., who has worked with end-of-life advocacy groups, said that no matter what the outcome in Yiambilis' case is, "he is going to punish himself probably more than the justice system will ever punish him."
"This is a situation where people, I'm sure, are already feeling guilty, and then to subject them to a criminal process is just hard for everyone," he added.