A Suffolk jury began deliberations on Tuesday in the trial of Michael McCarthy, the man accused of killing 2-year-old Bella Bond and dumping her body in Boston Harbor, a case that relies heavily on the testimony of the child’s mother.

The four women and eight men began their review after impassioned closings from both sides that zeroed in on the credibility of Rachelle Bond, a recovering heroin user who waited months before she told police about her daughter’s death in June 2015.

McCarthy’s lawyer, Jonathan Shapiro, focused on the contradictory aspects of her testimony, urging jurors to dismiss Bond’s “worthless word.’’

“Without her testimony, the prosecution has no case at all,’’ Shapiro said. “It was a web of lies. A changing web of lies.’’

In his closing argument, Suffolk Assistant District Attorney David Deakin implored the jury to look past Bond’s faults and to the evidence that connected McCarthy, 37, to Bella’s death.

“If you find him not guilty, you will be letting him get away with murder,’’ Deakin said.

The summations capped a four-week trial that featured 169 exhibits and 34 witnesses, eight of them for McCarthy’s defense.

Jurors have four options for a verdict: not guilty or guilty of first-degree murder, second-degree murder, or involuntary manslaughter.

The most pivotal witness was Bond, 40, who told jurors she saw McCarthy fatally punch Bella in the stomach in June 2015, then threatened to kill her if she told anyone.

Bond said McCarthy put the child’s body into a plastic bag, weighed it down with barbells, and threw it in the water. Her remains washed ashore on Deer Island in June 2015. For months, she was known only as “Baby Doe’’ as investigators conducted an international search to determine who she was. Bella was identified in September 2015, after a friend of McCarthy’s contacted the authorities to tell them Bond had accused McCarthy of killing her daughter.

During the trial, Shapiro asserted that Bond had killed the child, then lied to McCarthy and told him the state Department of Children and Families had taken the girl.

In a powerful moment of his closing argument, Shapiro reminded jurors of the recording McCarthy had made of him comforting the child, who had been having nightmares about monsters.

McCarthy told her to kill the monsters with love, Shapiro said.

“His advice did not work,’’ Shapiro said. “In the end, the monster came for this little girl — and it was her mother.’’

Deakin told the jury to remember another recording — that of investigators interrogating McCarthy in September 2015, when they finally learned Baby Doe’s identity.

During the 30-minute conversation, McCarthy, who was in a hospital room awaiting surgery, denied hurting Bella Bond. But Deakin told jurors they were listening to a man who had practiced for months what he would say to police, noting that McCarthy never sounded upset when investigators told him Bond had been killed.

“He made two critical errors,’’ Deakin said. “He forgot to act surprised about Bella, and two, he forgot to act concerned.’’

Deakin urged jurors to focus on the barbells, rusty weights that matched the ones found in McCarthy’s father’s plumbing shop in Quincy. McCarthy had a key to the shop, but Bond did not, prosecutors said.

He also told them to focus on texts that he said showed McCarthy’s attempts to control Bond, including a series of messages he sent her three weeks after Bond’s body was found. When Bond had to go to Housing Court, McCarthy urged her not to mention Bella, lest the DCF take her away. “We can’t lose her to the state,’’ he wrote her in July 2015. “We love her too much to ever let those vampires be around her.’’

Shapiro said the messages showed that McCarthy did not know Bella was dead. But Deakin said they were the calculated writings of a man who knew his phone might eventually be seized by police.

“He’s speaking in code, ladies and gentlemen,’’ Deakin told the jury.

Legal observers have called the prosecution’s case weak, citing the problems with Bond as a witness and the lack of physical evidence and an exact cause of death. Bond said Bella was beaten, but the medical examiner said that her account of the child’s injuries was unlikely to have led to the toddler’s death. The medical examiner testified Bella may have died from a blow to the chest or from asphyxiation.

In his closing argument, Deakin took that testimony into account, telling the jury that McCarthy may have either beaten or asphyxiated the child.

He said the day Bella’s body was discovered, signals from cellphone towers indicated that Bond and McCarthy had driven past the site where the child’s body was dumped, looking for police activity. That contradicted Bond’s assertion that she did not know her daughter’s body had been found until September 2015.

Bond pleaded guilty in February to being an accessory after the fact to murder. In exchange for her testimony, Bond, incarcerated since September 2015, will be credited with time served and get two years of probation. Shapiro reminded jurors of that, saying prosecutors made a “deal with the devil.’’

“Frankly, that disgusts me,’’ he said. “And I hope you feel the same way.’’

John R. Ellement of the Globe staff contributed to this report. Maria Cramer can be reached at mcramer@globe.com.