Alberta RCMP say a man investigated in the nearly two-month disappearance of two seniors is now considered a suspect.

Travis Vader had only been named as a person of interest in the case of the missing couple, Lyle and Marie McCann, until Tuesday.

"The positive progress in the investigation now validates Mr. Vader as a suspect," RCMP Sgt. Tim Taniguchi told The Canadian Press.

"I can't get into the specifics of the information received," he added. "Revealing the specifics of that information would be inappropriate and could put the investigation at risk.

"We still want the public's assistance to provide any information they have."

The missing couple's daughter, Trudy Holder, spoke to CTV News on Tuesday and asked whoever is responsible for her parents' disappearance to co-operate with police.

"Please step forward and help us end this nightmare and tell me where my mom and dad are," she said.

The McCanns, both in their 70s, were last seen on July 3, when they left their St. Albert home, near Edmonton, to visit family in B.C.

Two days later, their motorhome was found burning in a field near Edson, 200 kilometres west of Edmonton.

Some two weeks later, the SUV their motorhome was pulling was found in the Niton Junction area, where Vader lives.

Vader, 38, is in custody in Edmonton on unrelated charges. He was arrested on July 16 on an outstanding warrant and has been detained since that time.

Police have not said what led them to officially name Vader as a suspect in the McCann's disappearance.

Vader's sister said her brother came out of hiding from police in early July, saying he was too tired to keep living in the bush.

She said her brother is innocent.

"If you knew Travis as a person, you would know he would never harm or do anything to any innocent person," Bobbi-Jo Vader told reporters following his arrest.

The McCanns' family has raised more than $10,000 for a reward in the case.

The RCMP say they have 18 officers still working on the file.

With files from The Canadian Press