Paul Parker of the Salt Lake County District Attorney's Office reviewed the case but decided not to prosecute. Neither Sorensen nor her boyfriend was charged with a crime. Deputy District Attorney Bob Stott said there was insufficient evidence as to Alexandria's cause of death.

But shrinking from a prosecution in a case where the death is "undetermined" raises eyebrows among some in the child welfare community.

"Generally, if it's undetermined, that's a red flag that the death may be suspicious," said Kristin Brewer, director of the 3rd District Court guardian ad litem office, which represents children. With more evidence, she said, the medical examiner could amend his ruling.

Utah medical examiner Todd Grey could not comment specifically on Alexandria Sorensen but said an "undetermined" ruling still provides plenty of room for prosecution. Read the medical examiner's opinion in the report, he said. The details are all there, Grey said.

Salt Lake County sheriff's detective Danielle Mudrock said the circumstances, including Sorensen's past history, raised her suspicions. But she said there was no evidence to support wrongdoing, and no one in the home where the death occurred admitted to any.

"I think it could very well be positional asphyxia, but how do you prove that when you don't have anybody saying this is exactly what happened?" the detective asked.

This case underscores the difficulties investigating and prosecuting child deaths.

Witnesses are rare. Investigators rely heavily on explanations from parents or caretakers. Cases are largely circumstantial and often based on complex medical evidence.

The Utah Department of Human Services' Child Fatality Review Committee examined Alexandria Sorensen's death in June on the assumption she suffocated as her sister had six years earlier. The committee reviews a child's death if the family received child welfare services within a year prior to the fatality.

"The cause of death is pending the final report of the Utah state medical examiner," an executive summary reads, "but is thought to be 'possible suffocation/positional asphyxia.' "

Sorensen has been in the Salt Lake County Jail since Oct. 26, on forgery and theft charges she says are related to bad decisions and drug use.

Because of her history, Sorensen, 26, is in maximum security at the Salt Lake County Jail. She spends 23 hours a day in her cell and sleeps away as much of it as she can. She rises at 6 a.m. to eat breakfast but goes back to bed until noon. The rest of the time she whiles away reading Danielle Steel novels, writing, talking to her roommate and playing cards. In a recent interview at the jail, she said she did nothing to cause Alexandria's death. The baby, she said, was not in bed with her and her boyfriend.