As crews continue to search a bay off southeast Texas for clues as to how a Boeing 767 cargo plane nose-dived into shallow water, a cadaver dog found the remains of the third and final victim of the doomed flight. Sheriff Brian Hawthorne of Chambers County, Texas, said an identity has not been released.

Tuesday's development came days after the Houston-bound Atlas Air plane crashed Saturday, leaving a large "extremely hazardous" debris field along Trinity Bay, some 35 miles east of the city. Flight 3591 had three people on board. Authorities identified two victims so far: Conrad Aska, the 44-year-old first officer and co-pilot, and Sean Archuleta, a 36-year-old jump-seat passenger, according to Hawthorne.

The plane essentially disintegrated upon impact after losing radio contact approximately 30 miles southeast of Houston's George Bush Intercontinental Airport. Crews have been using airboats and helicopters to comb through the wreckage, where chunks of the plane can be seen across the muddy landscape.

Wreckage can be seen along Trinity Bay southeast of Houston, Texas. CBS News

Search for black boxes

A search for the black boxes was called a "high priority" Sunday by the National Transportation Safety Board (NTSB), which is on scene along with other federal agencies. NTSB said it has been difficult finding the flight data and voice recorder because they may be submerged deep in the mud, preventing the locator signal from working.

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Crews are bringing in heavy equipment to dig for the black boxes and to recover other debris from the crash, CBS affiliate KHOU-TV reports.

"The contractor is bringing in equipment specialized for shallow water. It's a barging system and they'll actually put equipment on top of it." Hawthorne said.

The mud is much like quicksand, KHOU-TV said, where someone could sink into it 1 to 2 feet deep very quickly.

CBS News

Surveillance video

The cargo plane had been carrying packages for Amazon's Prime Air service. It was on approach to Houston's airport when air traffic controllers warned the pilots they were approaching bad weather. NTSB said Monday video footage of the plane prior to the crash — captured by a camera from a jail about a mile away — won't be made public for quite some time as the investigation continues.

Victims mourned

Captain Sean Archuleta, who had been a pilot for Mesa Airlines since 2013 and had been riding in the aircraft's jump seat getting a lift back home in the Houston area.

The Associated Press said Archuleta's wife lives in Colombia and was "devastated" when she learned of the crash. He was a new father, AP reports, and was weeks away from starting his "dream" job flying for United Airlines, according to Don Dalton, Archuleta's roommate.

"This is a sad day for the entire Mesa Family as we mourn the loss of Captain Sean Archuleta," Jonathan Ornstein, Mesa's chairman and chief executive officer, said Sunday. "Our thoughts are with Sean's family, the families of the two Atlas Air pilots, and the whole Atlas Air organization. This is a loss for all of aviation."

The company has created a support program for the victims' families and that a team has been at the site of the crash helping investigators.

Jason Campbell was one of the civilian boaters at the site of the crash Saturday and described the grim scene.

"Pieces of bodies, nothing bigger than ... you know," Campbell told KHOU-TV. "It's obvious it's human pieces, but nothing bigger than you can hold in your hands."