Massachusetts investigators remain tight-lipped as they seek a motive and cause of death in the case of a 2-year-old girl after a mother and her boyfriend were charged in the her death Friday.

The toddler was identified as Bella Bond on Friday, almost three months after her remains were found in a trash bag that washed up on a Boston Harbor Beach. Suffolk County District Attorney Daniel Conley announced at a news conference he authorized a murder charge for Michael McCarthy, 35, and the girl’s mother, Rachelle Bond, 40, for accessory to murder after the fact.

However, Conley didn’t comment on how the young girl, who had no obvious signs of trauma to her body, died. He also declined to answer questions on a possible motive. “Why does anyone kill a 2-year-old child? What could she have done,” he asked.

Bella Bond, a chubby-cheeked, brown-eyed girl widely known as Baby Doe, had tugged the heartstrings across the country after authorities have urged the public’s help. Her image was seen by millions of Facebook users.

"At just shy of three years old, Bella Bond was a true innocent," Conley said at a news conference announcing the charges. "This child, whose very name means beauty, was murdered."

During the investigation, the National Center for Missing and Exploited Children created a composite image of what the girl might have looked like when she was alive. Within two weeks, the image had reached an estimated 47 million people on Facebook.

House Speaker Robert DeLeo, D-Winthrop, said Bond and McCarthy are blaming each other for the girl's death.

"It appears as though it was a situation of the boyfriend who was involved and apparently, I think, mother and boyfriend sort of blaming each other in terms of who harmed the child."

The Boston Globe reports Rachelle Bond told investigators that McCarthy had lashed out at the girl as being possessed or being a demon. She claims McCarthy punched Bella in the stomach until she went unconscious, the newspaper reports.

Conley said McCarthy was being treated for a medical condition at a Boston hospital unrelated to the case. Both Bond and McCarthy are scheduled to be arraigned Monday.

State child protection officials said they had contact with Bella twice, for four months in 2012 and three months in 2013. In both cases, officials described the involvement as “support for neglect,” and the cases were later closed.

Between 2001 and 2006, the Department of Children and Families terminated parental rights for two of her mother's older children. One of the children was later adopted by her maternal grandmother; the other was adopted by someone outside the family, DCF officials said.

The girl's body was found June 25 by a woman walking a dog. The Globe reports Bella's body was placed in a refrigerator before it was disposed of, according to officials briefed on the case said.

Despite the widespread publicity, a text tip line and billboards with the girl's image, investigators were frustrated for months as they tried to learn her identity. They got their big break after Boston police received a tip and a search warrant was executed Thursday at Rachelle Bond's apartment.

Bond had a history of drug and prostitution arrests.

On her Facebook page, she appears to be a doting mother, posting numerous photos of her daughter, who she calls "Bell" and "monkey."

On Sept. 15, 2014, a photo shows Bella wearing a tight-fitting, one-piece romper. "Look at my Bell," Bond wrote. "The outfit isn't supposed to be a catsuit ...Love her to death. I am on top of the world because of her. My life is complete again and worth living. I give her the world and more if I can..."

Conley said he received at least 10 offers from people who wanted to take care of the little girl's burial, including Cardinal Sean O'Malley.

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The Associated Press contributed to this report.