A woman who killed her pregnant neighbour by cutting the baby from her womb has apologised for the crime as she was sentenced to life in prison without parole.

Brooke Crews, who was convicted of murder, told a court she wished she could take the pain away from the victim’s family.

The details of how 22-year-old Savanna Greywind bled to death after Crews cut her were revealed for the first time at a hearing in North Dakota.

Crews, 38, had pleaded guilty to the crime, which officials had previously described as a “cruel and vicious act of depravity".

In tears, Crews read out a statement in court, which said: "There is no excuse. There is no rationalisation. There is nothing."

Ms Greywind, who is of Native American descent and lived in Fargo, disappeared on 19 August when she was eight months pregnant after leaving her family home to visit a neighbour.

Hundreds of people, including groups of Native Americans from nearby areas, helped to search for the missing woman.

After an eight-day search, the nursing assistant’s body was found wrapped in plastic in a river by kayakers, without the baby.

The infant was found at Crews’s house in good health. DNA confirmed it was Ms Greywind’s daughter.

The father of the baby expressed his grief at discovering how his girlfriend, who had lived in Fargo, had died. Ashton Matheny said the facts “tore me apart”.

The victim’s mother said she was pleased that her killer had received the toughest possible sentence.

Norberta Lafontaine-Greywind called the acts against her daughter "beyond evil" in a statement in court, adding that she has suffered nightmares since.

Her husband, Joe Greywind said they were finding it "near impossible" to heal, after the tragic events.

Defence attorney Steven Mottinger had asked for a lesser sentence for Crews, pointing out that she admitted guilt without any promise of leniency.

"Acceptance of responsibility is important," Mr Mottinger said in court. "It has to mean something."

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Crews initially claimed that Ms Greywind gave up her newborn daughter, but later admitted taking advantage of the woman to get the child, according to court documents.

Crews's boyfriend, William Hoehn, also faces a trial in May. He has pleaded not guilty. Prosecutors had cited his pending trial in withholding public details of Ms Greywind's death earlier.

Mr Hoehn told police he came home on 19 August to find Crews cleaning up blood in their bathroom. He said Crews presented him with an infant girl and told him: "This is our baby. This is our family."

Mr Hoehn told police he took garbage bags containing bloody shoes and his bloody towels and disposed them away from the apartment complex.

A bill in Congress aimed at protecting Native American women and girls from violence, abduction and human trafficking is being named after Ms Greywind.

Savanna's Act, introduced by Democratic Senator Heidi Heitkamp, would improve tribal access to certain federal crime information databases and create standardised protocols for responding to cases of missing and murdered Native Americans.

Additional reporting by Associated Press