The sinking of the Titanic has long been a cautionary tale about the dangers of hubris. But after more than a century, a new documentary offers evidence that the iceberg wasn’t the only reason for the sinking of the “unsinkable ship.” Instead, the floating mountain of ice may have happened to strike the exact spot where the hull had been weakened by a coal fire blazing in the bowels of the passenger ship.

In "Titanic: The New Evidence," which airs on the Smithsonian Channel on January 21, Irish journalist Senan Molony argues that the hull of the infamous ship was compromised weeks before it set sail. Through researching photos and eyewitness testimony from the time, Molony contends that a fire spontaneously lit inside one of the Titanic’s enormous coal bunkers and critically weakened a crucial segment of the ship’s hull.

"The ship is a single-skin ship," Molony tells Smithsonian.com. By that he means that while modern ships contain two hulls, at the time, the Titanic, like most ships of its day, just had the one. Because the bunkers where the crew stored coal for the engines sat right next to the hull, the heat from the fire would have transferred directly to the skin, damaging the Titanic's structure.

For Molony, who has spent decades studying the Titanic, the "smoking gun" came in a recent discovery of a trove of photographs documenting the ship’s construction and preparations for its maiden voyage. The photos had been taken by the engineering chief of Harland and Wolff, the Belfast-based company that built the doomed vessel. About four years ago, Molony and a collaborator purchased the photographs from a descendant of the company’s director, who had found them stored in an attic. As they pored over the images, Molony was shocked to see a 30-foot-long black streak documented on the outside of the Titanic’s hull, close to where the iceberg struck its starboard side.

“We asked some naval architects what this could be, and nobody knew and everybody was intrigued,” Molony says. “The best suggestion at the time was that this was a reflection." But Monology disagrees because, at the time the photograph was taken, he says, there was no road or dock on the shore which could have been reflected on the hull.

According to engineers from the Imperial College London, the streak in the photograph may have been caused by a fire in one of the Titanic’s coal bunkers—a three-story-tall room that stored much of the coal that fueled the ship’s engines. Molony believes that the fire had started as early as three weeks before the Titanic set out for its maiden voyage, but was ignored for fear of bad press and the desire to keep the ship on schedule.

“Britannia rules the waves,” Molony says. “They’d been facing massive competition from the Germans and others for the valuable immigrant trade. You don’t want don’t want a loss of public confidence in the whole of the British maritime marine.”

Just after survivors made landfall, several people who worked on the ship’s engines cited a coal fire as the cause of the shipwreck. An official inquiry by British officials in 1912 mentioned it, too, but Molony says the narrative was downplayed by the judge who oversaw it.

“He was a shipping interest judge, and, in fact, he presided at a toast at the Shipwrights' Guild four years earlier saying ‘may nothing ever adversely affect the great carrying power of this wonderful country,’” Molony says. “So he closes down efforts to pursue the fire and he makes this finding that the iceberg acted alone.”

Molony’s theory has its skeptics. Over the years, all sorts of people have offered up alternative theories to explain why the Titanic sank, ranging from being struck by a torpedo from a German U-boat to being brought down by an Egyptian mummy’s curse, Dan Bilefsky reports for The New York Times. While a coal fire is certainly more plausible than a murderous, undead pharaoh, others still contend that the iceberg was the decisive factor in the ship’s sinking.

“A fire may have accelerated this. But in my view, the Titanic would have sunk anyway,” Dave Hill, a former honorary secretary of the British Titanic Society, tells Bilefsky.

Still, Molony stands by his findings. After all, that same inquiry stated that the Titanic had sunk fully intact, while it was later found broken in half on the sea floor.

“Just because an official finding says it, doesn’t make it true,” Molony says.

Many details of what happened on that fateful night in April 1912 may be lost to history, but if nothing else, these findings present an interesting new angle to the infamous, and it would seem unsinkable, story.

Titanic: The New Evidence airs January 21 at 8 p.m. ET on the Smithsonian Channel.

Editor's Note, January 22, 2017: This story originally referred to the source of this new research as being from the Royal College of London. They are from Imperial College London.