A 35-year-old Dorchester man allegedly killed the cherubic 2 1⁄2-year-old girl who came to be known as “Baby Doe” because he “supposedly thought the child had demons in her,” a tipster in Billerica told police during a phone call Wednesday, breaking open a heartbreaking murder case that touched millions around the world.

Police records obtained by the Herald show the big break in the “Baby Doe” investigation came at 12:27 p.m., when an unidentified tipster told police the little girl’s mother, Rachelle Bond, had admitted to the caller’s brother that her boyfriend, Michael P. McCarthy, “killed her child.”

Working off of that information, investigators were finally able to identify the little girl, whose discarded body was found in a trash bag on Deer Island, as Bella Bond and arrest McCarthy, 35, on a murder charge and Rachelle Bond, 40, on a charge of being an accessory after the fact.

“It was a tip called into our offices at our homicide (unit), that really brought this case to where it is today,” Boston police Commissioner William B. Evans said yesterday. “We’re always out there saying any little information, no matter how little it is, it’s useful. I think we’re seeing that today.”

The “Baby Doe” case made international headlines after her body was found near the waterline by a passerby June 25. The computer-generated image of a little, brown-haired girl that was released by investigators and plastered on billboards across the state made the rounds on national news programs and had been viewed online by 60 million people, state police said earlier this month.

The media blitz resulted in tens of thousands of tips, investigators say, with leads coming in from across the country and from as far away as Europe.

The little girl’s grief-stricken father, Joseph Amoroso, told the Herald Bella was conceived in a tent at Occupy Boston and he left Rachelle Bond, his former girlfriend, after finding out she had been arrested for prostitution.

“That’s the story behind how me and Rachelle made this beautiful child,” Amoroso said of their Occupy Boston tryst, adding that he believes Bond had nothing to do with their daughter’s death.

“She told me the whole story,” Amoroso said. “She was very emotional, sincere through the whole thing, and I believe her. I believe her — that it was this man who murdered our daughter, murdered a 2-year-old.”

His daughter’s full name, Amoroso said, is Bella Nevaeh Amoroso Bond.

“Her name was Bella … This child, whose very name means beauty, was murdered,” Suffolk District Attorney Daniel F. Conley said during an emotional press conference yesterday. “At just shy of three years old, Bella Bond was a true innocent.”

Several times, Conley declined to provide further details on the case, deferring to McCarthy and Bond’s Monday arraignment in Dorchester District Court.

He also said that the state medical examiner was still working to determine a cause of death.

State Police Col. Richard McKeon praised the tireless work of investigators, who never gave up hope in their search for the one clue that would help bring those responsible to justice.

“These men and women who have investigated this case have given her name back,” McKeon said. “Now we will give her justice.”