Officials on Thursday confirmed the worst about the fate of the sub that went missing Sunday on a quest to take five people to view the wreckage of the Titanic. It had imploded, they said, likely just hours after it departed.
But during the course of the search, officials reported that they'd detected mysterious banging noises from below the ocean's surface. That left many people wondering: If the sub was already gone, what was responsible for those sounds?
Officials first said early Wednesday that they had detected underwater noises in the area of their search for the missing sub, the Titan, saying the sounds had been picked up over the course of Tuesday night and Wednesday. They were described as banging noises heard at roughly 30-minute intervals.
A Navy official later said the sounds were picked up by Canadian P-8 aircraft that dropped sonobouys — devices that use sonar to detect things underwater — as part of the international search effort.
Coast Guard Capt. Jamie Frederick said at the time, "With respect to the noises, specifically, we don't know what they are, to be frank with you."
Carl Hartsfield, an expert in underwater acoustics and the director of the Woods Hole Oceanographic Institution, whose team was helping with the search, said Wednesday there could be numerous possible explanations.
"The ocean is a very complex place, obviously — human sounds, nature sounds," he said, "and it's very difficult to discern what the sources of those noises are at times."
But when officials gave their grim update on Thursday, confirming that the sub's debris had been found in pieces on the sea floor after a "catastrophic implosion," a timeline began to emerge that indicated the sounds could not have come from the missing crew.
A U.S. Navy official said the Navy detected "an acoustic anomaly consistent with an implosion" shortly after the sub lost contact with the surface on Sunday, CBS News national security correspondent David Martin reported. That information was relayed to the Coast Guard, which used it to narrow the radius of the search area, the official said.
U.S. Navy analysis determined that the banging noises heard earlier in the week were most likely either ocean noise or noise from other search ships, another official said.
An undersea implosion of the sub would have destroyed the vessel nearly instantaneously, experts explained, leaving the passengers no opportunity to signal for help.
"In a fraction of a second, it's gone," Will Kohnen, chairman of the professional group the Marine Technology Society Submarine Committee, said in an interview with Reuters.
"It implodes inwards in a matter of a thousandth of a second," he said. "And it's probably a mercy, because that was probably a kinder end than the unbelievably difficult situation of being four days in a cold, dark and confined space. So, this would have happened very quickly. I don't think anybody even had the time to realize what happened."
Numerous videos have gone viral on social media that claim to contain audio of the sounds officials heard during the search. The audio appears to be sonar beeps, followed by what sounds like knocking and then clanging noises. One video on Tiktok has amassed more than 11 million views and prompted many to question the information coming from search officials.
However, the audio is not related to this event. A spokesperson for the U.S. Coast Guard, which was leading the international search effort, told the Associated Press that they had "not released any audio in relation to the search efforts."
Li Cohen is a social media producer and trending content writer for CBS News.