Santo Thomas, Mexico - More details about the three bodies recovered in Mexico's Baja California state, believed to be those of two Australian brothers and an American who disappeared on a surfing trip, emerged Saturday.

The bodies were in an "advanced state of decomposition" when they were hoisted out of a shaft a few steps from the edge of the Pacific Ocean cliff, said state prosecutor Maria Elena Andrade.

But "given their clothing and certain characteristics such as long hair and specific physical descriptions, we have high probability," that the remains are in fact those of the three missing men, she said.

Another body found at the site had been there longer and was unconnected to the latest disappearances, officials said.

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Andrade said one line of inquiry is whether the deaths resulted from an attempt to steal the tourists' pickup truck. The vehicle, which had been burned, was found nearby.

AFP journalists saw the authorities use a pulley system to extract the mud-covered bodies from the shaft on Friday near the town of Santo Thomas, about 30 miles southeast of Ensenada, a spot that is difficult to reach but popular with surfers.

The grisly discovery appeared to confirm the worst fears of the families and friends of holidaying Australian brothers Callum and Jake Robinson, and their American friend Jack Carter.

The Australian brothers' mother Debra Robinson had sounded the alarm on a Facebook page for Baja California tourists several days ago, after they dropped out of contact.

Callum Robinson's Instagram showed various shots from the trio's Mexico trip: enjoying beers with their feet up in a bar, lazing in a jacuzzi, eating roadside tacos, looking out at the surf.

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Six-foot-four Callum had played in the US Premier Lacrosse League, which left a message on its website saying the lacrosse world was "heartbroken by the tragic loss" of the trio.

Jake Robinson was a doctor in Perth, Australian media said.

Mexican authorities, who have arrested three suspects, were carrying out the investigation in collaboration with the FBI and the Australian consulate.