Last year, a purported transcript of communications between the Titan submersible and its mother ship circulated widely on the internet. Viewed millions of times, the so-called log suggested that a series of alarms had turned a dive to the resting place of the Titanic into a heart-pounding crisis in which the five voyagers struggled in vain to return to the surface.

But the head of the U.S. federal government team investigating the disaster said that the entire transcript is a fiction. After nearly a year of investigation, his group has found no signs that the five voyagers aboard the Titan had any warning of the catastrophic implosion that was to take their lives. Two miles down, where seawater exerts vast pressures, an implosion would have made the violent collapse of the vehicle’s hull instantaneous.

“I’m confident it’s a false transcript,” said Capt. Jason D. Neubauer, who retired from the U.S. Coast Guard and serves as chairman of the Marine Board of Investigation, the agency’s highest level of inquiry. “It was made up.”