WATERVILLE, Maine — Investigators put up crime-scene tape around the home of the father of a 20-month-old girl who has been missing since last weekend and two of the state’s top homicide prosecutors were called to the house Thursday as the search for her entered its sixth day.

Meanwhile, national experts not associated with the case said the chances that Ayla was abducted are slim.

But Waterville Police Chief Joseph Massey insisted that Ayla Reynolds’ disappearance remains a missing child case, that “everything remains open and we’re not discounting anything.” Massey told reporters that the investigation is now focused on an expanded search of the house in a neighborhood of neatly kept tract homes.

“That is the last place Ayla was seen. So as you might expect we’re going to give a lot of attention to that particular house, looking for any clues where she might be or where it would help us to locate her,” Massey said.

“We need to go through that as thoroughly as we can, just like we do in any other investigation.”

He said officials from the state attorney general’s office, including criminal division chief William Stokes, were at the house, but that was just to give them an opportunity to look at the site.

“We’re at a point where we thought it was appropriate for him to come in and just do a walk-through,” Massey said.

Attorney General Spokeswoman Brenda Kielty said the visit to Ayla’s father’s home by Stokes and Andrew Benson, another top homicide prosecutor, was “standard protocol.” She declined further comment on the case.

The police chief played down the significance of yellow tape strung about the perimeter of the small property, saying it was “just an additional barrier” to secure the site. He said people shouldn’t read too much into the presence of a state police incident command van parked there, saying it was for the convenience of technicians working at the site.

The investigation continued in other parts of the central Maine city, including at the airport where cadaver dogs were brought in, as well as streams and waterways. By Thursday, police had received more than 200 tips from the public, all of which were being followed up and some rechecked, the chief said.

Ayla was living with her father, Justin DiPietro, who reported her missing Saturday morning. DiPietro told police he last saw her when he put her to bed the previous night. He said she was wearing green pajamas with polka dots and the words “Daddy’s Princess” on them. She also had a soft cast on her broken left arm.

Ayla ended up with her father after child welfare workers intervened while her mother, Trista Reynolds, checked herself into a 10-day rehabilitation program. Reynolds, who completed the rehab, had filed court papers that she hoped would lead to the return of her daughter. The filing came the day before Ayla was last seen.

The case drew expressions of community support and hope the child will be found safe as more than 60 people, many of them mothers with young children, gathered at a local church Wednesday night for a candlelight vigil.

Massey said he believes police have made “significant progress” even through Ayla has not been found.

“There are a lot of things that we’ve eliminated, and that’s just as important as identifying things,” he said.

Dr. David Finkelhor, a University of New Hampshire sociology professor and director of the university’s Crimes Against Children Research Center, said Thursday that although his knowledge of the case is limited to what has been reported in the media, it’s highly unlikely that Ayla was abducted from her home.

“The majority of abductions occur with children over the age of 10,” said Finkelhor, whose research has included compiling reports for the U.S. Department of Justice and other agencies on missing child cases.

“The main motive for abduction is usually sexual assault,” he said. “You find rather few offenders who are looking for a child that young [as Ayla Reynolds] for sexual gratification. In the absence of any evidence of abduction, the more likely scenario would be family maltreatment or homicide.”

Finkelhor said that a study he did in 1999 showed that around 100 children were abducted by their parents annually, and that that number has probably declined in the past decade. In contrast, the study showed that children killed by family members number as much as 1,500, according to Finkelhor.

“Unfortunately, those are concentrated among younger kids,” he said. “It just gives you a sense of how much more likely it is that parents are involved in foul play.”

Finkelhor said detectives involved in Ayla’s case are likely investigating several scenarios at once — including the possibilities that Ayla simply wandered away from her home during the night or that she is being hidden with a family member or friend.

“If the parents didn’t have anything to do with it, it adds insult to injury,” he said. “Not only has their child been ripped from their lives and under the most dire circumstances, but they’re being considered as suspects. It’s incumbent on the police to investigate every angle.”

“It is a possibility that one of the parents arranged to have the child spirited off somewhere in order to deal with the custody issue or to prevent the other parent from gaining custody,” he said. “In which case, someone is taking good care of the child.”

Finkelhor said investigators are likely to have explored that possibility and that most families have a “tight circle of close confidants” who would be found by police in relatively short order.

Ayla’s case has attracted national attention, including a segment Thursday morning on the Today Show. Clint Van Zandt, a retired FBI profiler, told a national audience that he sees several causes for concern in Ayla’s case and indications that she was likely not abducted. Among those factors are that according to her father, she was sleeping in a bedroom with another child who was not abducted and that it would be very difficult for a perpetrator to enter the family’s small home and take a child without being detected. He also said he found it implausible that no one checked on Ayla for a nearly 12-hour period between when she was put to bed and discovered missing. Van Zandt said a key part of the investigation is trying to determine who other than DiPietro witnessed Ayla being put to bed.

“Is it plausible [that she was abducted]? Yes,” he said. “Is it possible? Yes. … Law enforcement knows the odds are more important when you think of the people within the house and closest to the child as opposed to an unknown offender. That’s why you do a two-track investigation.”