Boulder County District Attorney Stanley L. Garnett was unable to file a murder charge under state law, and he highlighted how the coroner found that the fetus didn't show any signs of life outside the womb, Garnett said.
The victim, Michelle Wilkins, 26, who was seven months' pregnant, survived this month's attack, which occurred when she went to a Longmont home to buy baby clothes advertised for sale on Craigslist.
"Now, I understand that many in the community -- and heaven knows I've heard from a lot of them -- would like me to file homicide charges," Garnett told reporters.
"However, that is not possible under Colorado law without proof of live birth. A prosecutor cannot file murder charges when a baby who is killed has not lived outside the body of the mother. For similar reasons, I cannot bring charges of child abuse resulting in death," the district attorney said.
The fetus' lungs never inflated, Garnett said. The fetus' exact cause of death, however, isn't immediately known and is expected to be revealed when the final autopsy report is released in six to eight weeks, he said.
Wilkins and her partner, identified only as Dan, named the female fetus Aurora, the prosecutor said.
Lane, 34, appeared briefly in a holding room during an initial court appearance Friday, but she didn't enter the courtroom. Her attorneys waived a formal reading of charges at the hearing, which occurred before the prosecutor's press conference.
"She could get a long sentence and very well could die in prison," the district attorney said about Lane, adding he couldn't immediately calculate the maximum number of years she faces if convicted of all counts.
Lane was also charged with two counts of crime of violence, two counts of first-degree assault, and two counts of second-degree assault, Garnett said.
Lane's next court date, a preliminary hearing, is May 5. She is being held on a $2 million bond.
Earlier Friday, the Boulder County Coroner's Office said the fetus wasn't alive on its own after it was cut from Wilkins' womb.
The female fetus didn't exhibit "any signs of life outside of the womb, therefore the circumstance is not being considered a live birth," Coroner Emma R. Hall said in a statement.
Friday's finding came a day after prosecutors indicated that Lane wouldn't face a murder charge
in the March 18 assault.
Wilkins was released from the hospital
on Thursday, relatives said.
The coroner's office performed an autopsy on the fetus and said Wilkins was 34 weeks pregnant.
"An autopsy has been completed," Hall said. "At this time neither the autopsy or the investigation have provided any evidence that the baby exhibited any signs of life outside of the womb, therefore the circumstance is not being considered a live birth. No evidence of trauma or injuries were found on the body.
"Final autopsy results will be released once all testing and further studies are complete," Hall said.
The coroner's finding apparently contradicts earlier claims made in police reports
that the fetus "gasped" and that emergency room personnel described the fetus as viable.
David Ridley, the 35-year-old husband of Dynel Lane, told police he found his wife "covered in blood" in the family home and later found "a small baby lying in the bathtub," a Longmont police report said.
"He rubbed the baby slightly then rolled it over to ... see it take a gasping breath," the report said.
Ridley took the baby and his wife to the emergency room of Longmont United Hospital, and the hospital told police the baby "would have been viable," the police report said.
But on Friday, District Attorney Garnett said that Ridley altered his earlier statement to police.
Without referring to Ridley by name, Garnett cited how media accounts took note of the police report and how a "witness observed Aurora taking a gasping breath."
"However, upon a more thorough examination of this witness by the Longmont Police Department, the witness clarified that Aurora was still and her mouth was open, but she was not breathing, which is consistent with medical evidence from the autopsy," Garnett told reporters.