AUGUSTA, Maine — Thursday marks the fourth anniversary of the disappearance of Waterville toddler Ayla Reynolds — perhaps the most publicized unsolved missing person case on the books in Maine.

Even though investigators presume that Ayla died four years ago, and her mother, Trista Reynolds, was one of the many family members of unsolved homicide victims who petitioned for the creation of the state’s first cold case squad, the new unit will not review her case, according to Stephen McCausland, spokesman for the Maine Department of Public Safety.

“It’s not a cold case,” McCausland said Wednesday. “It’s been actively followed for four years and it continues to be an open and active case. It’s the largest criminal investigation in state police history. It continues to be worked on actively.”

Ayla was 20 months old when she was reported missing from her grandmother’s Waterville home on Dec. 17, 2011. At the time of her disappearance, Ayla was staying with her father, Justin DiPietro, and his then-girlfriend Courtney Roberts of Portland. Also in the house were Roberts’ son and DiPietro’s sister Alisha DiPietro and her daughter.

“We believe they have not given us the full story,” McCausland said six weeks into the investigation when authorities released information about the toddler’s blood being found inside her grandmother’s home.

“Nothing has changed,” McCausland said Wednesday, referring to the limited cooperation of the three adults at the home when Ayla reportedly disappeared.

Maine State Police, working in conjunction with the Waterville Police Department and the Maine Warden Service, launched the largest missing person search in the state’s history, on water and on land, to no avail.

Investigators ruled out the possibility that Ayla was abducted and said her disappearance was a result of foul play. No arrests have been made.

Assistant Attorney General Lara Nomani, who is tasked with reviewing the state’s unsolved homicides, said two years ago that she was reviewing Ayla’s case as a missing person-suspicious death. Such cases do not arrive on her desk until they are at least approximately two years old, Nomani said at the time. Messages left Wednesday for Nomani were not immediately returned.

“The attorney general’s office has been involved in this investigation from day one,” McCausland said. “The AG’s office has been a significant component of the investigation.”

Over the last four years, more than 1,500 tips have been followed by police and people with information continue to call, McCausland said.

“We still get leads on a regular basis,” McCausland said. “Although they are fewer than a few years ago.”

“At least one-third” of the tips have been from people claiming to be psychics, which are now mostly disregarded, he said.

The total cost for investigating Ayla’s disappearance is high, but McCausland didn’t have the exact figure at his fingertips, especially given that multiple agencies, and the FBI, have been involved in the case.

“The cost, frankly, is irrelevant,” McCausland said.

This week, Trista Reynolds, in a Facebook post, asked residents to light a pink light on Thursday and every day until Jan. 1, 2016, in memory of her daughter.