LARGOCarrie Hendrickson could hear her granddaughter's tiny voice coming from the other side of her son's closed bedroom door Thursday."Grandma! Grandma!" the two-year-old cried. "Milk, water. Milk, water."Just the day before, a Child Protective Services caseworker had told her 25-year-old son, William Hendrickson III, to keep the door open — warning him that the room was too hot for the toddlers who lived in the room with him. Now Hendrickson could hear her granddaughter quietly sobbing on the other side of the door.She opened the door and yanked the girl into the kitchen. Then William slammed it back shut — bolting himself and his 8-month-old son inside.Carrie called her son's caseworker. When she arrived with police about an hour later, they found baby William Hendrickson IV's body gray and lifeless in a playpen."It's my greatest heartbreak that I wasn't able to get him out," Carrie Hendrickson said. "I am going to have to live with the rest my life knowing my son was able to shut that door."Her son, she said, didn't have the air conditioner in his room plugged in. A large fan sat on his bed, also unplugged. Officials said the room got up to 109 degrees. The baby's body temperature was 105.6 degrees.[ READ MORE: Largo police: Father told day before baby's death not to leave him in hot bedroom ]On Thursday, William Hendrickson III was arrested on charges of aggravated child neglect for the condition of his daughter and aggravated manslaughter in the death of his son.Carrie Hendrickson, 60, and her husband, William "Bill" Hendrickson Jr., 60, say that they invited their son to move into their home in January because they were worried about his children. They hoped to teach him how to be responsible and ensure the children were safe, they said.Instead, the modular home on S Belcher Road became plagued by arguments. Carrie called the police the night before her grandson died. Her son had threatened her after she told him she was going to call child services, she said."This didn't have to happen," Bill said, two days after his grandson was carried out of their home under a white sheet. "It was avoidable and preventable, and now we can only ask people to pray for our grandson's soul." • • •The week before baby William died, life in their home began falling deeper and deeper into chaos.The children's mother, Elizabeth Michelle Rutenbeck, 24, was arrested on battery charges for assaulting Carrie, after a fight over $5 and an Xbox escalated, according to a police report.Rutenbeck ripped their bedroom door off the hinges, Carrie said. She's still being held in Pinellas County Jail on the battery charges.In response, William refused to let his children leave his room, his parents said. He slept with three stubby knives under his pillow.Child services had been in and out of the family's home since William and Rutenbeck moved in, the parents said. In a statement, the Florida Department of Children and Families said there had been three separate investigations into how William and his girlfriend treated their children.The grandparents didn't have custodial rights of the children, but thought if the babies were in their home, they could keep them safe. Bill wanted to teach the young couple how to be adults, to manage their lives. The kitchen and living room would be their responsibility: 900 square feet total, complete with a tiny bedroom with turquoise walls and their own bathroom. There was a second bedroom for the 2-year-old, Solara, though William never wanted to set it up, his dad said.The grandparents lived in a separate room, on the other end of the house, with its own bathroom. They let them stay for free."The house was set up to be baby safe," Bill said. Bill has a big air conditioning unit in the living room to keep the whole house cool. The two main bedrooms have smaller units for Florida's hottest nights. But even air conditioners sparked arguments in the tension-ridden home. William left his bedroom's unit on 24 hours a day, till it shorted out and stopped working, his dad said, ignoring requests that he give it breaks throughout the day.William, his parents said, would sit on his bed playing video games, talking to people over his headset rather than to his own children. He never took them to the pool or playground on the complex's property. He and Rutenbeck didn't do dishes and seldom cooked. The dishes piled up in their room in their room and attracted bugs. Bill and Carrie thought if they refused to clean up after them, it would show child services that the young couple needed help. Bugs eventually took over the small bedroom they lived in.Bill and Carrie didn't always have an adversarial relationship with their son. Bill said the trouble started when his "toxic relationship" with Rutenbeck began about three years ago. The family is Native American and raised their son to follow some of their traditions. But as William grew up, Bill said, he pushed away from believing in God. He seemed depressed and at times suicidal.He never grew out of playing video games, his father said, and seemed only to watch violent television. His dad, who spent his years working to protect Indian burial grounds, would preach love. His son, the dad said, would call him a "hippie" and tell him the world didn't work that way.• • •A child service worker came to the home on Wednesday, to discuss whether William's latest case could be closed, according to a document the Hendricksons showed the Tampa Bay Times. That would mark the end of William having to complete visits with caseworkers.His mother and father told the caseworker the case should remain open. They said William was leaving out important details, which they told the caseworker. His girlfriend was in jail. His children weren't going to day care. He wasn't working."He's a good liar," his mother said. "He put on an act."The meeting ended with the situation unresolved, William's parents say.Before she left, the caseworker demanded he keep the door open so the children wouldn't get overheated. Later that morning, when the door remained closed, Carrie told William to open it. William threatened her, she said, and she called 911.They came and left, Carrie said. Nothing felt solved. It turned out, it wasn't. On Sunday afternoon, Carrie started cleaning out her son's old room. She and Bill hadn't been allowed in since July. They were surprised by how bad it had gotten. There were cracker crumbs and roaches. Carrie and Bill had bug spray and bombs, but William refused to use them, they said."I hope he rots in hell," she said. "He murdered my grandson." After their son left in handcuffs and their granddaughter was taken to the hospital and then placed with relatives, Bill took a closer look at the air conditioner his son told police didn't work. He plugged it in. It blew cold air."How did we give birth to such a monster?" Carrie asked.Contact Sara DiNatale at [email protected]Correction: Carrie Hendrickson called 911 on Wednesday morning. The wrong time was listed in a previous version of this story.