WATERVILLE, Maine -

A 20-month-old girl who vanished a week before Christmas after being put to bed in her father's home was taken away and didn't walk out on her own, investigators said yesterday as they announced the largest reward ever offered in the state to help find a missing person.

It marked the first time since the search for Ayla Reynolds began that police have directly said that they don't believe that she left the house by herself.

"At this point in the investigation . . . we are confident that Ayla did not walk out of the house by herself," Waterville police Chief Joseph Massey said at a news conference, at which he announced that a $30,000 reward was being offered for help finding her. "We believe that someone was involved in taking her out of the house, and that's where the focus of this investigation has turned."

The reward was gathered with donations from residents and businesses in the Waterville area, state Department of Public Safety spokesman Steve McCausland said.

Massey said that the developments in a mystery that's been featured on national television programs have not shifted the matter from a missing-person case to a criminal investigation. Despite the passing of the Christmas holiday with no sign of Ayla, police remain committed to finding her, the chief said.

"The intensity of the investigation is as high today as it was the first day," he said. "We continue to employ every single resource we have."

Massey was joined at the news conference by Waterville attorney John Nale, who appealed for the safe return of Ayla.

"I ask and I plead with the person or persons who have Ayla Reynolds that they please keep her safe and return her safely to us," Nale said.

Hundreds of police officers, game wardens and local residents have been searching for Ayla since she was reported missing by her father, Justin DiPietro, on the morning of Dec. 17. Massey said that a report about the case on the Fox network television program "America's Most Wanted" during the weekend generated some leads, which are being checked by police.

DiPietro told investigators that he last saw Ayla when he put her to bed the night before at his home in Waterville, a city of 16,000 residents about 20 miles north of the state capital, Augusta. He said that she was wearing polka-dot pajamas with the words "Daddy's Princess" on them and had a 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 said she hoped would lead to the return of her daughter. The filing came the day before Ayla was last seen.

DiPietro has said that he has "no idea what happened to Ayla or who is responsible." He said last week that his family and friends would do "everything we can to assist in this investigation and get Ayla back home."