PORTLAND, Maine (AP) — Crime scene investigators returned to the central Maine home from which a 20-month-old girl disappeared as police announced that they believe foul play was involved. Two weeks after Ayla Reynolds went missing, evidence technicians from Massachusetts joined Maine State Police crime scene investigators on Friday at the Waterville home where the girl was last seen by her father. The home 75 miles north of Portland now sits empty, surrounded by yellow crime scene tape. Hours later, Waterville police Chief Joseph Massey announced Friday night that the case "has evolved from the search for a missing child to a criminal investigation." In a statement, the chief said the conclusion was based on evidence that has been gathered over the past two weeks, but he didn't elaborate. He said state police would take the lead on the investigation. "All of our efforts continue to locate Ayla. Although this is beginning the third week, we remain hopeful," Maine Department of Public Safety spokesman Stephen McCausland said. Ayla's father, Justin DiPietro, told police he last saw her when he put her to bed the night of Dec. 16. He reported her missing when she was nowhere to be found the following morning. Before she vanished, Ayla was wearing green polka dot pajamas with the words "Daddy's Princess" on them and had a soft cast on her broken left arm. Extensive searches of woods, waterways, fields and private properties around Waterville, a city of 16,000 residents, have failed to turn up anything. The day after Christmas, investigators announced a $30,000 reward, the largest ever for a missing person case in Maine, for information leading to Ayla's whereabouts. McCausland on Friday declined to discuss whether any of the 300-plus leads had borne fruit for investigators. He also declined to talk about suspects or evidence that has been gathered. He saidDiPietro and Ayla's mother, Trista Reynolds, of Portland, were cooperating with investigators. http://www.inorthfacejackets.net/north-face-mens/men-s-gore-tex-jackets/north-face-men-s-gore-tex-jacket-orange-grey.html There were news reports Friday that two cars seized from the Waterville home were returned to DiPietro and an unidentified woman. McCausland declined to confirm those reports. Investigators put up crime scene tape at the father's home last week. Outside the home, teddy bears and stuffed animals were piled at a makeshift shrine. Ayla was placed in her father's care while her mother was in a substance abuse rehabilitation program, which she completed. Trista Reynolds, making an appeal on national television on Thursday, said that she had questions for DiPietro but that he had not returned her calls since their daughter went missing. She previously raised concerns about Ayla's treatment while in her father's care after the girl broke her arm, an incident described by police as an accident. She had no further comment Friday night, her sister said. DiPietro couldn't be reached for comment. The Associated Press has been unable to find a telephone listing for him, and the house where he stayed is now empty. http://www.inorthfacejackets.net/north-face-mens/men-s-gore-tex-jackets/north-face-men-s-nuptse-down-vest-red.html A few days before Christmas, DiPietro, addressing the public for the first time, said in a statement he had "no idea what happened to Ayla or who is responsible." Later, in another statement, he said, "I would never do anything to hurt my child." Former FBI profiler Clint Van Zandt said Friday that the odds of finding a child lessen if he or she isn't found within the first day or two of disappearing. But he said there's always reason for optimism, noting that there are even rare cases of missing children who turn up years later in someone's care. "If you don't get this child back real quickly, you know that it gets harder and harder," he said. "But you can't give up hope."