(NewsNation) — Almost one year after a search for the missing Titan submersible ended with tragedy, a new documentary reveals more details about the rescue effort and the eerie knocking sounds heard by searchers.

The Titan lost contact with its support vessel early in a dive to visit the wreck of the Titanic with five people on board. The search lasted for days, only to end with evidence the craft had suffered a catastrophic implosion during the initial dive.

One piece of evidence that kept the search going was a series of knocking sounds captured by underwater monitoring equipment from the Royal Canadian Air Force.

A new documentary from executive producer Jeremy Daldry examines the search effort and includes new audio of the noises.

“The reality is, nobody quite knows what those knocking sounds were,” Daldry said on “NewsNation Now.” “The ocean is a very busy place, especially the deep ocean. It’s full of currents and tides, debris — and water is a very good conduit of sound. Sound can travel great distances in water.”

Even without knowing where they originated, the noises were enough for searchers to keep looking. The hope that passengers could be rescued drove searchers even though some were already considering an implosion.

“Some of the rescuers believed the sub had imploded when they stopped getting communication from it,” Daldry said. “But yet we know that there were these noises that were kind of encouraging.”

In hindsight, Daldry said it’s easy to see the slim chances the sub had but rescuers were operating on a philosophy of taking any chance to save the divers.

“In the rescue community, you never leave someone behind if there’s a chance they can be rescued,” he said.

For Daldry, the biggest takeaway from the disaster is that deep sea exploration, while important, needs to be regulated for the safety of all involved.