LONDON — Maybe it wasn’t just the iceberg.

Ever since the Titanic sank more than 104 years ago, killing more than 1,500 men, women and children, mystery has swirled around the tragedy.

No one doubts that the ship collided at high speed with an iceberg off the coast of Newfoundland.

But a new documentary posits that the sinking of the ship — hailed at the time as the largest ever built, and praised for its professed unsinkability — may have been accelerated by a giant coal fire in its hull that appeared to have started as long as three weeks before it set off on its fateful journey to New York from Southampton, England.

In the documentary, which was broadcast on Channel 4 in Britain on New Year’s Day, Senan Molony, an Irish journalist who has spent more than 30 years researching the Titanic, contends that the fire, in a three-story-high bunker next to one of the ship’s boiler rooms, damaged its hull, helping to seal its fate long before it slammed into the iceberg.

“It’s a perfect storm of extraordinary factors coming together: fire, ice and criminal negligence,” he argues in the documentary, “Titanic: The New Evidence,” which will air in the United States on the Smithsonian Channel on January 21. “The fire was known about, but it was played down. She should never have been put to sea.”