TOLEDO, Ohio - For the past three years, Mandy Hayes had counted on her mother to care night and day for three of her children after another son at home had become too much to handle.

When she decided it was safe to bring all of them back home in recent weeks, her mother snapped, killing her three young grandchildren and herself with the help of her 32-year-old son who also died, police said.

Letters left behind indicate 54-year-old Sandy Ford and her son Andy son carefully planned the murder-suicide by barricading the garage in their Toledo home, nailing plywood over the windows and then running two hoses from the exhaust of his pickup truck into the rear window of a car where all five were found dead, police said.

Police are waiting for autopsy results.

The family disagreement over where the children should live erupted within just the past week, with police and children services workers being asked to intervene. But both said there was never any indication that the dispute would end in tragedy.

Firefighters using a sledgehammer broke down the garage door to find the bodies of 5-year-old Madalyn Hayes, her 6-year-old brother Logan and 10-year-old sister Paige slumped inside a car, along with their grandmother and uncle. Two hoses attached to the exhaust of a pickup truck pumped gas fumes through the car's rear window.

Police said letters inside the house indicated the woman and her son plotted the murder-suicide, beginning by picking up the children from school Monday morning after their mother had dropped them off earlier.

Toledo police Sgt. Joe Heffernan wouldn't say what was in the letters, but it appeared some were written by the children.

"We're trying to figure out all the why's in this," he said.

Authorities were called to the home by the children's frantic grandfather after he discovered the letters and was unable to force open the garage door. Despite the grisly scene, investigators found no signs the children were forced into the car and believe all five died of carbon monoxide poisoning.

Until last week, the children had spent the last three years living with their grandparents, Sandy and Randy Ford, and their uncle at a house in a residential neighborhood close to the Michigan state line.

Mandy Hayes had asked her mom for help caring for the three children because a fourth child was becoming disruptive, said children's services representatives and a family friend.

"She was just being protective," said the friend, Cammie Turner.

While the children were living with their grandparents, their parents saw them almost every day and went on outings to parks and the zoo, Turner said.

"Their kids mean everything to them," she said.

But recently Hayes had decided they should all return home, and the children moved back in with their parents last week, upsetting Hayes' mother, Turner said.

"Mandy wasn't taking the kids away from her entirely," she said. "She wanted them home. It wasn't like she was taking them and grandma could never see them again."

Turner said Hayes had confided that her mother was controlling, but she never seemed alarmed by it.

"It doesn't make sense," she said. "I can't imagine. To have your mom...."

Police were at the house last week and children services workers met with both sides of the family, most recently on Saturday, said Dean Sparks, executive director of Lucas County Children Services.

"We only know that there were a lot of allegations back and forth," he said, adding that Sandy Ford was worried about placing her grandchildren back in the home with their 9-year-old brother, who had been disruptive in the past.

Mandy Hayes and her husband also have a baby who was born just less than a year ago.

But the agency had no authority to decide who should keep the children, Sparks said, and the parents had every right to bring them back into their home.

Turner said she never saw any indication of a strained relationship between Hayes and her mother, and they never went to court over the issue of custody.

Family members declined to comment.

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Associated Press writer Kantele Franko in Columbus, Ohio, contributed to this report.