Ottawa police say the investigation into the stolen Winston Churchill portrait taken from the Fairmont Chateau Laurier in August is still active, and that they will "exhaust" all avenues in efforts to solve the case.

The portrait, captured in December 1941 by Canadian photographer Yousuf Karsh during the Second World War, went missing from the hotel between and was replaced with a copy.

Police are appealing for the public's assistance in the theft.

"Central Investigations has spoken to potential witnesses at the Fairmont Chateau Laurier, the public and professionals in fields surrounding Mr. Karsh's work," Ottawa police told CTV's Your Morning in an emailed statement. "We have actively followed up on leads from the public that have been received online, by phone and by email."

Hotel staff noticed in August the portrait was not hung properly and the frame did not match others from Karsh's work also seen in the Chateau Laurier's Reading Loung.

Police say they cannot confirm whether a suspect or any person of interest have been identified to date.

"It was missing for a certain amount of time before they realized that it had been taken," analyst Robert Wittman, creator of the FBI's National Art Crime Team in the U.S., told CTV's Your Morning on Thursday. "As a result, the thieve, or the thieves, who took it had a head start."

Wittman, a now former FBI agent, said he has worked on investigations that took decades to close. To him, the ongoing investigation is not "surprising" given the period of time before the fake portrait was found and the case started.

"At this point, they're (police) doing the forensics, they're still continuing with that, probably checking out surveillance," Wittman said. "I think that this particular theft was an inside job. What we found in the United States is that approximately 90 per cent of thefts from institutions in museums are insider jobs."

Ottawa police told CTV's Your Morning in a statement they are, "actively investigating this matter and will continue to do so until every investigative avenue is exhausted."

The police are aware of the historical importance and personal connection this portrait has to the community.

"The Ottawa Police Service takes all criminal complaints seriously and this case will remain open until it is solved," police said in the statement TO CTV New's Your Morning.

Wittman says the criminal(s) would need the opportunity and understanding of how security at the Chateau Laurier works. They would also need tools and time to pull off the heist.

The famous photograph that decorates the reverse side of The Bank of England's £5 note and famous for Churchill's wartime expression, . Christopher Marinello, founder and CEO of Art Recovery International, previously told Â鶹ӰÊÓ Channel, a copy print of the portrait sold at auction for about $81,000.

"I think the value is important because it's going to come back at some point unless it's destroyed, which we hope it isn't," Wittman said. "The piece will come back to market, and when it does, that's when they'll recover it."

To date, tips from the public have led police to copies of the portrait said Wittman.