Blood was found in the Maine home from which a 20-month-old toddler, according to her father, disappeared on Dec. 17, ABC affiliate WCVB reported.
Ayla Bell Reynolds' father, Justin DiPietro, told police last month that he believed his daughter was snatched from the bedroom of the Waterville home she shared with him between her 8 p.m. bedtime and when he checked her bedroom in the morning.
Within days, however, what began as the search for a missing child turned into a criminal probe after investigators discovered blood in the basement of the home, a fact which is only now being made public.
Releasing that detail earlier "would have interfered with the investigation," said Stephen McCausland, spokesman for the Maine Department of Public Safety.
Forensic investigators are still working to determine the source of the blood and how long it had been in the basement.
Both DiPietro, 24, and Trista Reynolds, 23, Ayla's mother, who does not live in the home and was forced by Child Protective Services to place Ayla in DiPietro's full-time care when she checked into rehab, have taken police-administered lie-detector tests.
Reynolds told WCVB that the test administrator concluded that she could not complete the test because of a medical condition.
DiPietro has said publicly that he passed the test, though Maine State Police would not comment on his claim.
Reynolds previously alleged that her daughter was bruised the last time she saw her, though DiPietro countered that those claims amounted to "accusation and insinuations."
"I would never do anything to hurt my child," he said.
"Daddy's Princess" was inscribed on the polka-dotted pajamas Ayla was wearing when she disappeared. Also, she wore a soft cast to protect a broken left arm.
No one has been charged in the case, which has included law enforcement's aerial and foot searches of an icy river near DiPietro's home and the draining of a local stream. The searches have yielded no clues. A $30,000 reward is being offered for information leading to Ayla.
"We remain hopeful that we will bring her back to her home," public safety spokesman McCausland said.