After a mother and her boyfriend were charged in the murder of the woman's 2-year-old daughter, investigators are not ready to speculate on a motive or even a cause of death.

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.

At a news conference Friday, Suffolk District Attorney Daniel Conley said he authorized a murder charge for Michael McCarthy, 35, and the girl's mother, Rachelle Bond, 40, for accessory to murder after the fact.

But Conley would not comment on how the young girl, who had no obvious signs of trauma to her body, died. He also declined to comment on a possible motive, asking "Why does anyone kill a 2-year-old child? What could she have done?"

A composite picture of the chubby-cheeked, brown-eyed girl, known before Friday as only Baby Doe, had tugged at heartstrings across the country after authorities asked for 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."

The girl was named Baby Doe by investigators who launched a massive social media campaign to find out who she was and how she died.

Using photos of her remains, 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 of the girl 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."

Conley said McCarthy was being treated at a Boston hospital for a medical condition unrelated to the case.

Both Bond and McCarthy are due to be arraigned on the charges Monday. Neither could be reached for comment.

Officials from the state's child protection agency 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.

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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Associated Press writers Collin Binkley, Bob Salsberg and Steve LeBlanc contributed to this report.