LAS VEGAS (KLAS) — As Lake Mead’s water levels receded and human remains nearly 50 years gone surfaced, a half-century-old investigation has returned to the spotlight.

Donald Smith, 39, from North Las Vegas, vanished during a boat ride at Lake Mead near Calville Bay in April 1974.

Documents obtained by Nexstar’s 8newsnow.com show Smith had left his home at around 1 p.m. on the day of his disappearance. His wife said Smith had been drinking, but that he wasn’t drunk. She said he had taken his handgun with him and had loaded a shotgun into the cabin of his boat.

About two hours later, two of Smith’s longtime friends, floating 150 feet away from his boat, said they saw him fall back into the lake with his hands thrown up. About one minute later, they said they arrived at where Smith had dropped into the water and found one deck shoe floating on the surface.

After diving in to search for him, they said Smith was nowhere to be found.

They also were not able to find Smith’s weapons on the boat or in his vehicle.

Investigators questioned Smith’s friends, but investigators determined it wouldn’t have been possible for anyone to conceal the weapons since rangers were present at the location. Instead, investigators said it was likely that the guns were stolen from Smith’s vehicle, which had been left unlocked. That kind of theft was common in the area at that time.

After searching for two days, investigators determined the water was too deep to thoroughly search the lake. The National Park Service didn’t have enough resources and precise information on where Smith drowned was unavailable.

They concluded that Smith either slipped or was knocked off balance by a wave. The coldness of the water and Smith’s breath being knocked out of him caused him to go underwater without leaving a trace of bubbles – or any other trace, investigators said.

Nearly 50 years later, water levels in Lake Mead were much lower. In October of 2022, a diver found a human bone in the mud near the fuel dock at Calville Bay, the same area where Smith disappeared. Over the next few days, National Park Service divers found a pair of jeans, more remains, and a wallet and credit cards belonging to Smith.

In late 2022, the maximum depth of that area, when Smith’s remains were found, was documented at 47 feet. In 1974, that same area was as deep as 160 feet.

Four sets of human remains have been found in Lake Mead since May 2022.

Larry Millwood is the proprietor of 3rd Reef Divers based in Henderson, Nevada, which offers diving training. He believes there may be additional human remains yet to be unearthed in Lake Mead. Although Millwood insists that he is not actively seeking out such findings, he and his crew are equipped to handle the situation should it arise.

“If we do happen to come across something,” said Millwood. “We’ll mark it and then let the authorities know.”

Millwood and fellow diver Mitchell Claffey say they haven’t personally found remains. However, they have made some discoveries, including weapons.

The weapons the divers found weren’t believed to be connected to Smith’s disappearance. The whereabouts of his guns remain a mystery to this day.