A woman convicted of killing her pregnant neighbour by cutting the baby from her womb has told a court her boyfriend had pressured her to "produce a baby" after figuring out she had lied about being pregnant.

Brooke Crews, of North Dakota, said she had concocted a phony pregnancy to keep from losing William Hoehn, who is on trial for conspiracy over the death of 22-year-old Savanna Greywind in August 2017.

Hoehn has admitted helping to cover up the crime, but says he did not know Crews had planned to kill Ms Greywind and take her baby.

Crews said Hoehn appeared surprised when he entered the bathroom in their apartment and discovered she had cut Ms Greywind's baby from her body.

Crews said Hoehn then retrieved a rope and tightened it around Ms Greywind's neck, saying: "If she wasn't dead before, she is now."

Hoehn spoke regularly with his lawyer, Daniel Borgen, during Crews' evidence but showed little emotion. Crews was crying and sniffling throughout.

Crews described her relationship with Hoehn as rocky and violent, saying it was fuelled by drugs and alcohol. She said they broke up at one point, and that is when she lied to him about being pregnant. She went as far as to email him a phony positive pregnancy test and ultrasound photo.

In early August, Hoehn told Crews he did not believe she was pregnant and said she needed "to produce a baby". Crews said she believed this was "an ultimatum".

"I took that to mean I better have a baby, no matter how it happened," Crews said.

Crews originally told police that Ms Greywind had given her the child. She later told officers they had argued and that she pushed Ms Greywind down and knocked her out before cutting her open.

A medical examiner testified on Monday that there was no evidence of head injuries.

Crews stuck to her story on Tuesday, saying she pushed Ms Greywind, who was knocked out when her head hit the bathroom sink. Crews said that is when she got a knife and began cutting the baby out.

Crews said the couple kept ropes in the house because Hoehn liked to tie her up during sex, including tying one around her neck. She also said Hoehn expressed fantasies about killing people and Crews said she initially told him she would be interested in that too.

The medical examiner who performed the post-mortem, Victor Froloff, said on Monday that he is not sure whether Ms Greywind died from blood loss or strangulation.

Crews pleaded guilty to murder and is serving life in prison without parole. She said she has no agreement with prosecutors for a lesser sentence in exchange for testifying.

Online Editors