Dan Herman, a State Police detective, was standing in the vestibule outside Courtroom 906 in Suffolk Superior Court on Wednesday, waiting for testimony to resume in the case he has lived and breathed for two years.

Herman was the chief investigator into the mystery of Baby Doe, the 2-year-old girl whose body was dumped into Boston Harbor like so much trash, the beautiful, star-crossed girl who turned out to be Bella Bond.

While Herman stood outside the courtroom, Michael McCarthy, the man charged with murdering Bella, took his seat at the defendant’s table. McCarthy’s all cleaned up now. The stringy junkie hair is now neatly trimmed. He’s put on some weight and fills out the gray suit that has become his trial uniform.

For a man who faces the prospect of spending the rest of his life in prison, ­McCarthy looks awfully comfortable, almost confident. At one point, after listening in on a sidebar discussion that his attorney, Jonathan Shapiro, and the lead prosecutor, David Deakin, had with Judge Janet Sanders, McCarthy returned to his seat wearing a wide grin.

McCarthy acts like a man who knows he has a chance to beat the rap.

Herman, the other State Police detectives assigned to Suffolk District Attorney Dan Conley’s office, and Winthrop police officers did extraordinary work after Bella’s body washed up on Deer Island. They did not rest until they found out who she was and what was done to her.

But they have no magical powers to alter facts, and the fact is that the time that passed between Bella’s death and the discovery of her body and identity left the prosecution at a big disadvantage. The exact cause of death is murky. There is no DNA, no trace evidence, no video corroborating Bella’s demise and the dumping of her body.

And the most glaring fact is that the case against McCarthy rests primarily on the word of a woman who, at the very least, participated in the disposal of her daughter’s body and the coverup of her own child’s murder.

Rachelle Bond says McCarthy, her live-in boyfriend, beat Bella to death because he was convinced Bella was possessed by demons. She says she went along with ­McCarthy’s diabolical coverup because she was deathly afraid of him.

Michael Sprinsky, a friend of McCarthy’s since childhood, testified that Bond told him the same thing Sept. 16, 2015, three months after Bella’s body was found. Sprinsky and his sister went to police, leading to Bella’s identification, and his testimony helps the prosecution by showing that Bond’s version of events was out there even before her arrest.

But Sprinsky also helped the defense, raising doubts about who was capable of beating Bella. He testified that Rachelle Bond shared McCarthy’s bizarre belief that Bella was possessed, that Bond spanked Bella “because Bella wouldn’t tell her about the demons that were inside of her.’’

Deakin acknowledged the prosecution’s challenges.

“The evidence will show you that most of the major players in this case had damaged themselves with drugs,’’ he said in his opening argument.

Even as Sprinsky helped the defense, Shapiro questioned the reliability of his memory, given that Sprinsky was shooting heroin, taking pills, and washing them down with 3 or 4 pints of vodka a day.

It’s hard to believe Rachelle Bond pulled all this off herself, so it’s hard to sit and listen to Shapiro insist that Michael McCarthy is innocent. But one thing Shapiro said about Bond is undeniably true: “Without her testimony, the Commonwealth has no case.’’

And so the jury — nine women and six men — and the rest of us await the testimony of Rachelle Bond.

Either she is lying to hide her own culpability in her daughter’s death, or she really was so beaten down by drugs, fear, and self-loathing that she did nothing while Bella’s body cooled in her kitchen refrigerator, awaiting a watery grave.

Either way, justice for Baby Bella rests on the credibility of the mother who failed her.

Kevin Cullen is a Globe columnist. He can be reached at cullen@globe.com.