BOSTON (AP) — A mother was arrested and her boyfriend was charged with murder in the death of a little girl whose body was found inside a trash bag on a Boston Harbor island this summer and who became known as Baby Doe, a prosecutor said Friday after a monthslong campaign to learn the girl’s identity.

Suffolk District Attorney Daniel Conley said that he authorized the murder charge for the boyfriend, Michael McCarthy, and that the mother, Rachelle Bond, was under arrest for accessory to murder after the fact.

The girl became known as Baby Doe as investigators trying to find out who she was and how she died launched a massive social media campaign including a composite sketch of her, showing her chubby cheeks and brown eyes. Her real name was Bella Bond, prosecutors said Friday.

“At just shy of 3 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,” he said.

After Baby Doe’s body was found in June, police immediately appealed to the public for help. The National Center for Missing and Exploited Children, using photos of her remains, created a composite image of what she might have looked like when she was alive. Within two weeks, the image had reached an estimated 47 million people on Facebook.

Photos of Bella posted on her mother’s Facebook page looked strikingly similar to the composite image.

Conley didn’t comment on a possible motive behind the girl’s death.

“That’s always a perplexing matter for us,” he said. “Why does anyone kill a 2-year-old child? What could she have done?”

State House Speaker Robert DeLeo said Bond and McCarthy were blaming each other for the death.

McCarthy, 35, was being treated at a hospital for a medical condition unrelated to the case, prosecutors said. Bond, 40, was in custody. Neither could be reached for comment on the charges. They are due to be arraigned Monday.

Officials from the state’s child protection agency said they had contact with Bella twice, for four months in 2012 and for 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 Bond’s older children. One of the children was later adopted by her maternal grandmother; the other was adopted by someone outside the family.

A spokeswoman for the Executive Office of Health and Human Services, Rhonda Mann, said the agency had been working with law enforcement to help police identify Baby Doe.

“Now that we know her name, the story is no less tragic,” she said.

Baby Doe’s body was found June 25 inside on Deer Island in Winthrop by a woman walking a dog.

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

Conley would not say how the girl’s body got to Deer Island but implied her mother placed it there. He said evidence led authorities to charge the mother with being an accessory to murder after the fact.

Bond, who has a history of drug and prostitution arrests, appears on her Facebook page to be a doting mother, posting numerous photos of Bella, whom she calls Bell or Monkey.

In a posting on Aug. 18, 2014, Bond wrote: “My Bella loved her birthday party and all the awesome things she got. Broke the bank on it but it’s all worth it to see her happy and laughing and smiling.”

A few weeks later, 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.”

Conley said he received at least 10 offers from people, including Cardinal Sean O’Malley, who wanted to pay for the little girl’s burial. He would not comment on how the girl died but said more information may be released when McCarthy and Bond are arraigned.

(Sarah Himes)