The mother of murdered baby Bella Doe testified against her ex-boyfriend, the man accused of killing the toddler, in Boston for the fourth day on Wednesday.

Rachelle Bond, 41, told a courtroom how Michael McCarthy was an avid follower of pro-Trump radio host Alex Jones and that he had become obsessed with conspiracy theories and the occult when he killed two-year-old Bella in June 2015.

McCarthy, 37, thought government workers were 'shape-shifters', she said and that he was pushing his 'off the wall' beliefs on to her.

Appearing in a smart blue shirt and suit jacket, Bond wept as she gave her testimony.

Rachelle Bond wept in court on Monday as she testified against her former boyfriend who is accused of murdering her two-year-old daughter Bella in 2015

'These were his conspiracy theories about the government. He was trying to make me believe this,' she said, according to The Boston Herald which reported from the trial.

Bella's body was found washed up on Deer Island, Massachusetts, in a plastic bag in 2015.

She was referred to as Baby Doe for months until a family friend identified her.

As part of a deal with the authorities, her mother is being spared jail in exchange for testifying against McCarthy.

She is currently behind bars but will be freed after the trial and under the condition that she pleads guilty to accessory after the fact.

If a jury however rejects her claims, she could face perjury charges and be sentenced to life imprisonment.

Bond previously told the court how McCarthy was 'obsessed' with the occult and believed Bella was a 'demon' before he killed her.

Michael McCarthy, 37, (left in court this week) is charged with murdering the toddler who police took two months to identify in 2015. After they found her decomposing body, they issued this computer generated image of her (right) to try to find her identity

Two months after she was found, a family friend came forward to identify Bella

She claims he took her life by punching her on the head, leaving her little body to go limp and gray.

Afterwards, she claims he told her: 'It was her time to go'.

Both she and McCarthy had been using heroin around the time of Bella's death. Giving evidence this week, the girl's mother said her memory of her death was clearer now that she is sober.

McCarthy denies killing the toddler and his lawyers insist that any sinister obsession with the occult was Bond's and not his.

They have consistently pointed to the diary Bond kept before her daughter's death. In it, she described her beliefs that politicians raped and killed children then drank their blood.

Bella's body was found by a walker in a trash bag on Deer Island on June 25, 2015.

Bella's mother is being spared jail in exchange for pleading guilty to accessory after the fact and testimony against McCarthy. Her appearance in court on Monday was vastly different from her arrest in 2015 (right)

She claims she went along with disposing of her daughter's body because she was afraid of her ex and was battling heroin addiction

Authorities found a duffel bag and weights which had been used to keep it in the water nearby.

McCarthy denies murdering the toddler

Without any indication of identity, authorities created a computerized image of what they believed she would have looked like before facial decomposition.

The photograph was circulated in Boston and she was referred to as Baby Doe.

Eventually, in September that year, a family friend who had been staying with McCarthy and Bond at their apartment, came forward.

They told how they'd witnessed the pair abusing Bella and said the child hadn't been seen for months.

Neither McCarthy nor Bond ever reported her as missing.

Bella's body was found in a tied-up plastic trash bag on Deer Island in Massachusetts on June 25