For years, authorities wondered about the identity of a U.S. Marine who appeared at the World Trade Center on September 11, 2001, helped find two police officers buried in the rubble, then vanished.

Even the producers of the new film chronicling the rescue, “World Trade Center,” couldn’t locate the mystery serviceman. The only name he’d given at the scene was “Sergeant Thomas.”

The puzzle was finally solved when one Jason Thomas, of Columbus, Ohio, happened to catch a TV commercial for the new movie a few weeks ago as he relaxed on his couch.

His eyes widened as he saw two Marines with flashlights, hunting for survivors atop the smoldering ruins.

“That’s us. That’s me!” thought the New York native, now working as a court officer in Ohio’s Supreme Court.

Sergeant Thomas, 32, hesitantly reemerged last week to recount the role he played in the rescue of Port Authority police officers Will Jimeno and Sergeant John McLoughlin, who were entombed beneath 20 feet of debris when the twin towers collapsed.

Now a father of five, Sergeant Thomas had been out of the Marine Corps for about a year when the terrorists struck. He was dropping one of his daughters off at his mother’s Long Island home when she delivered the news.

“My mother insisted it must be an accident,” he said. Sergeant Thomas believed differently.

Rushing to his car, he dug in his trunk, retrieved his Marine uniform and put it on.

Minutes later, he was speeding toward Manhattan, eventually finding himself on the West Side Highway following a convoy of police cars.He had just parked when one of the towers collapsed.

“All I saw was ash. Ash coming in my direction,” Sergeant Thomas said.

As it billowed around him, he knelt by the side of his car and pulled his shirt up over his mouth.Then, he got up and ran at the center of the cloud.

“Someone needed help. It didn’t matter who,” he said. “I didn’t even have a plan. But I have all this training as a Marine, and all I could think was, ‘My city is in need.'”

Sergeant Thomas spent hours putting people on stretchers and setting up triage stations before bumping into another ex-Marine, Staff Sergeant David Karnes. Sergeant Karnes also grabbed his fatigues and headed into Manhattan when he learned of the attacks.

Acting on their own, the pair decided to search for survivors. Carrying little more than flashlights and an infantryman’s shovel, they climbed the mountain of debris and began an hours-long hunt, skirting dangerous crevasses and shards of red-hot metal, calling out “Is anyone down there? United States Marines!”

It was dark before they finally heard a response.The two crawled into a deep pit to find Sergeant McLoughlin and Mr. Jimeno, injured but alive.

Even then, getting help wasn’t easy. SergeantThomas clambered back to the surface and feverishly tried to flag down other rescuers in the dark. Sergeant Karnes phoned his sister in Pennsylvania and had her relay their location to 911 dispatchers. Mr. Jimeno would spend 13 hours in the pit before he was pulled free. Sergeant Thomas stayed long enough to see him come up, but couldn’t find the strength to wait for Sergeant McLoughlin, who remained pinned for another nine hours.

“I was completely exhausted. I just had to get out of that hole,” Sergeant Thomas said.

He stumbled away and drove home, stopping to hose himself off in his backyard. “I knew my wife would kill me if I went in to the house with all that ash,” he said.

Thomas said he returned to ground zero every day for another 2 1 /2 weeks to pitch in, then walked away and tried to forget.

“I didn’t want to relive what took place that day,” he said.

Thomas said it might take a little while before he is ready to see “World Trade Center”the film, but encouraged others to see it.

The movie’s producer, Michael Shamberg, said Sergeant Thomas and Mr. Jimeno had a reunion by telephone last week and have made tentative plans to meet in person.

Mr. Shamberg said he apologized to Sergeant Thomas for an inaccuracy in the film: Sergeant Thomas is black. The actor who portrays him, William Mapother, is white. Mr. Shamberg said the filmmakers didn’t realize the mistake until after production had begun.

Asked about the error, Sergeant Thomas laughed and gently chided the filmmakers, then politely declined to discuss it further.