(CNN) -- Maine police revealed Saturday that blood was found in missing toddler Ayla Reynolds' basement and, for the first time, cast doubt on the accounts of adults who were in the home when she was last seen -- saying they don't "pass the 'straight-face' test in Maine."
"We feel they know more than they're telling us," said Stephen McCausland, a spokesman for the Maine Department of Public Safety.
Investigators found the blood during their initial search of the Waterville, Maine, house, though they did not specify how much blood there was and where exactly in the basement it was located. Determining whose blood it is is "a top priority of the crime lab," McCausland said.
Justin DiPietro -- the father of Ayla, who was 20 months old when authorities began looking for her last month -- sleeps in the basement of the home, which is owned by his mother.
McCausland said authorities felt they should reveal the information about the blood discovery now, because "we need information from the public, and we think this might help."
"The public needs to understand we're frustrated, and no closer to finding Ayla than we were ... December 17," he said.
Police have said that DiPietro's mother, Phoebe DiPietro, wasn't home the night of December 16, when her son told police that he put his daughter to sleep in her first-floor bedroom at 8 p.m. He called police the next morning just before 9 a.m. to report her missing.
Justin DiPietro has said in a written statement that "he would never do anything to harm my daughter."
Police now say that Ayla was alone in the bedroom the night before she was reported missing, even though relatives have told CNN her younger cousin normally slept in the same room.
In addition to Ayla and her father, two other adults and two other children were in the house on the night of December 16, according to authorities. They were Justin DiPietro's girlfriend and her young son, plus Ayla's aunt and her toddler. The latter two also live in the house.
The two other children are thought to have slept in a different bedroom than Ayla, and police believe Ayla's aunt was with them, according to McCausland.
Police said the adults told them "someone snuck into the house, went into the bedroom where Ayla was sleeping, and no one heard or saw anything." Yet "there is no evidence that we have found that would point to an abduction," said the state spokesman.
"Their story ... doesn't pass the 'straight-face' test in Maine," McCausland said.
"We don't know what happened other than we know Ayla didn't walk out on her own, and we have grave doubts she was abducted because there were three adults in the home that night (and) it's a very small house."
No one has been arrested in the case, and police have not identified Justin DiPietro or anyone else as a suspect.
"We're not ruling anyone in or anyone out," McCausland said.
Police confirm that Justin DiPietro took a polygraph test, but won't reveal the results. Lie detector evidence is not admissible in court. He told Waterville's Morning Sentinel newspaper that police wouldn't show him the actual polygraph paperwork to show him how he did.
"I know I went in there and smoked it," Justin DiPietro said. "I told the truth, and that's it."
Phoebe DiPietro has told CNN she fully supports her son and doesn't believe anyone who was in the house on that December night would harm the toddler or had anything to do with her disappearance. She has said she just wants Ayla back healthy and safe.
"I'd give everything I owned if we can have her back," Phoebe DiPietro said.
On Saturday, Justin DiPietro and Ayla's mother, Trista Reynolds, appeared together publicly for the first time since their daughter's disappearance to thank those who have tried to help locate Ayla, CNN affiliate WCSH reported.
The two embraced when DiPietro showed up 30 minutes before the event ended and later talked calmly on the steps of Waterville City Hall, according to WCSH.
Trista Reynolds had told HLN's Nancy Grace last month that she raised Ayla for 18 months, and that DiPietro had become involved after she "needed to go and get a little bit of help for myself." She told HLN she entered rehab.
DiPietro had sole custody of Ayla when she disappeared. Two days before Ayla was reported missing, Reynolds filed court documents seeking custody of the girl. The 23-year-old mother said she didn't tell DiPietro she was going to court because he was "vindictive" and "verbally abusive."
Reynolds said Saturday that "I don't have the answers that you guys are looking for." She reacted emotionally, when asked about the police announcement that blood was found in Ayla's house.
"I'm ready to go knocking at people's door myself because I want to know what happened to my daughter, and I want to know where she is and who took her or just whatever, like everybody else does," she said.