When Jim Crabtree learned last May that his mother and wife had been shot by his father, who then committed suicide, he felt not horror, but relief.
Crabtree had been struggling to take care of his 62-year-old wife, Rita, who was diagnosed with Alzheimer's disease six years earlier. His parents were able to watch after her each day while he was at work. But his mother, 80, was forced to use to a wheelchair with severe joint pain and arthritis and his 84-year-old dad had begun to develop dementia.
"My father shot my mother and then he shot my wife and then he shot himself," Crabtree told NBC's Maria Shriver. "It sounds like a horrible violent end, but in actuality it was an euthanasia that my father did. It was a great gift that my father was able to give me. He ended my Alzheimer's and elder care issues at once."
Like many Alzheimer's caregivers, Crabtree felt stretched to the breaking point.
"It's the kind of stretch you get living your life on a treadmill," he said. "Just when you think you got things in order, something else comes up and you have to run a little bit farther and a little bit faster, but you never get ahead. You're just scrambling around trying to figure out how you're going to solve all these problems."
Although rare, there are other murder-suicide cases involving caregivers and their charges. It's a sign of how stressful the job is, said Linda Ercoli, director of geriatric psychology at the Semel Institute at the University of California, Los Angeles.
"It's like having a second job that is 24-7 on top of whatever else you're dealing with in life," she told NBCNews.com.
Even his job as an emergency room nurse didn't prepare 55-year-old Jim Crabtree for the overwhelming triple burden of caring for a wife with Alzheimer's, a father descending into dementia and a mother with crippling arthritis.
Those burdens are so great they can shave years off the life of caregivers, experts say. In fact, one study showed that compared to others, caregiver spouses aged 66 to 96 had a 63 percent higher mortality rate, Ercoli said.
"Unlike many other types of things, Alzheimer's comes with an uncontrollability that really extracts a price," said Dr. Richard Schulz, a professor of psychiatry at the University of Pittsburgh Medical Center. "And there is a vigilance component from having to be on guard all the time. That in and of itself can be very stressful."
Add to that the length of time caregivers are on the job – on average eight years, but sometimes as long as 20 – and you've got years of chronic stress, Ercoli said.
Making matters worse, the demands of caregiving often result in social isolation as caregivers disconnect from other family and friends because they feel they have no time to keep up these relationships, Schulz said.
Under that heavy burden a caregiver's emotional state can bounce from helplessness to exhaustion to anger. And that anger can be directed toward the patient if the caregiver doesn't understand the disease well enough to realize that some of the annoying behaviors are simply symptoms of illness.
The high levels of anger and frustration often felt by caregivers is one reason Ercoli suggests all guns be removed and sharp objects be locked up. Violence isn't uncommon in homes where an Alzheimer's patient is being cared for, the geriatric psychologist said. Studies have found that while about 5 percent of caregivers are sometimes violent with their charges, nearly 16 percent of patients are sometimes violent with their caregivers.
That's not the only risk caregivers face. Along with a higher death rate, they also are at increased risk of immune system problems and cancer.
And then there's the ever-mounting stress, which many caregivers don't recognize since they're so caught up in the day-to-day survival.
"You can go to the Alzheimer's Association [website] and actually take a test to find out how many signs of caregiver stress you have," Ercoli said. "It can be very eye opening."
While many derive satisfaction caring for a loved one in the early stages of the disease, that satisfaction can dwindle as Alzheimer's progresses, robbing patients of their personalities, Schulz said. "People talk about the loss of self," he explained. "The person you used to know disappears and for many people that is a really distressing aspect. They don't recognize the person any more."
That rings true for Crabtree, who said "Rita at the end was an empty vessel," one he nevertheless had to care for. Until his father ended her life – and his own.
Crabtree said other caregivers have empathized with his situation – and the relief he felt.
"They'll come up to me … quietly [and] say, ‘Jim I'm really sorry, but you know, I'm kind of envious … You got out easy. You didn't have to go the last mile,'" he said.
Reactions like this are more understandable when you consider the strain on caregivers' mental health. Some 40 percent to 70 percent suffer from depression, Ercoli said. And in others, the stress boosts anxiety. Treatment for anxiety and depression can ease a caregiver's distress, but often people don't feel comfortable asking for help.
"People kind of just take it," Ercoli said. "They don't even share with their doctors."
Experts say caregivers need to reach out to others for support – whether it's help in caring for the patient or just with house cleaning and shopping for groceries. But even with help, caregiving is the toughest job most people will ever have.
"People don't say, ‘I survived Alzheimer's,'" Crabtree said. "We are the survivors. I survived caregiving."