LARGO, Fla. (WFLA) – A 62-year-old woman who was artificially inseminated and gave birth to a baby girl 13 days ago, is now charged with her daughter’s death, after detectives say she left her 6-year-old son alone with the baby and he beat her to death.

Pinellas County Sheriff Bob Gualtieri on Thursday outlined the disturbing details in the bizarre and gruesome case saying he’d “never seen anything like this.”

Kathleen Marie Steele, 62, was charged with aggravated manslaughter in connection with the death of her infant daughter, Kathleen Steele.

Gualtieri said that Steele had left the baby alone in a van with her six and three year-old sons while she went into a cell phone store to have her cell phone repaired.

“Frankie and Phillip, at 6 and 3, were running amok, unsupervised, and what others saw was consistent with what happened on Monday, and that she didn’t care for the kids and was negligent and neglectful and abused them by leaving these kids in the car, the sheriff said.

While the boys were alone with their little sister in the van, the baby started crying. Gualtieri said the 6-year-old boy took the baby from her car seat, shook her and slammed her head against the ceiling.

“The best way I can describe it to you is he pummeled her,” said the sheriff. “He was tossing that baby around like a rag doll.”

“One of the worst things I’ve ever seen, with especially a 13-day-old, and her appearance was just one of that had been pummeled,” he added.

When Steele returned to the van, her 6-year-old son told her that the baby was in distress. However, Steele drove to a car rental business where Gualtieri said she went inside for 30 minutes to renew the contract for the van she was renting.

Later, the son said again the baby was in distress. Gualtieri said Steele called a neighbor, who is a nurse. The nurse went to the motel and checked the baby, who appeared to be dead. The nurse then called 911.

Paramedics responded and tried to revive the baby. The sheriff said Steele did not appear to be concerned about her daughter’s condition. While rescue crews were trying to revive her infant daughter, Steele was putting groceries away in the kitchen.

“She was very aloof about it,” said Gualtieri.

The sheriff said that an autopsy showed the baby girl suffered severe head trauma and had multiple skull fractures.

Gualtieri said Steele was a widower with two children who became pregnant using artificial insemination before giving birth to her daughter. He said she was “ill-equipped to have a baby.”

The sheriff said the 6-year-old boy admitted to injuring his sister and described what happened to detectives. Gualtieri said that detectives found the baby’s blood on the ceiling of the van.

The 6-year-old boy will not be criminally charged. He and his younger brother are in DCF custody.

“It’s a very sad case to say the least,” said Gualtieri.