Loch Ness monster hunter is still looking for an answer

Twenty-five years after he headed one of the biggest ever hunts for the Loch Ness monster, scientist Adrian Shine says he is still determined to find a logical explanation for his discoveries.

In October 1987, Shine was in charge of Operation Deepscan.

A line of boats fitted with advanced deep sonar scanners, swept the entire area of the loch over the course of three days.

The scanners showed up what looked like three large moving objects deep below the surface.

The sonar contacts remain unexplained.

"It could have been a seal, or Atlantic sturgeon entering the loch," he told Witness on BBC World Service. "But why would they be swimming so deep down?"

Video production by Daniel Gordon.