Mexican authorities say two Australians and an American were killed on a surfing trip because thieves wanted the tires from their truck. 

The latest details in the case come after a fourth body was discovered during a search for the missing men in Baja California. State prosecutors have not officially confirmed the identities of the missing men, but have said the victims’ family members are viewing the bodies to see if they can be identified by sight.

The corpses were found decomposing after the thieves dumped them into a remote well about 50 feet deep, some four miles from where the men were killed, authorities said. The well also contained a fourth cadaver that had been there much longer.

Chief state prosecutor María Elena Andrade Ramírez said the probability that the corpses belong to the missing men is "very high," noting that they still appeared to be identifiable by sight. "If they say that they are not completely certain that it is their relative, we would then have to carry out genetic testing."

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The three men, brothers Jake and Callum Robinson from Australia and American Jack Carter Rhoad, were on a camping and surfing trip along a stretch of coast south of the city of Ensenada when they went missing last weekend.

Andrade Ramírez theorized the killers drove by and saw the foreigners' pickup truck and tents and wanted to steal their tires. But "when [the foreigners] came up and caught them, surely, they resisted."

She said that's when the killers would have shot the tourists.

The thieves then allegedly went to what she called "a site that is extremely hard to get to" and allegedly dumped the bodies into a familiar well. She said investigators were not ruling out the possibility the same suspects also dumped the first, earlier body in the well as part of previous crimes.

"They may have been looking for trucks in this area," Andrade Ramírez said.

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The thieves allegedly covered the well with boards. "It was literally almost impossible to find it," Andrade Ramírez said, and it took two hours to winch the bodies out of the well.

The site where the bodies were discovered near the township of Santo Tomás was near the remote seaside area where the missing men's tents and truck were found Thursday along the coast. 

On Sunday, dozens of mourners, surfers and demonstrators gathered in a main plaza in Ensenada, the nearest city, to voice their anger and sadness at the deaths.

"Ensenada is a mass grave," read one placard carried by protesters. "Australia, we are with you," one man scrawled on one of the half-dozen surf boards at the demonstration. A woman held up a sign that read "They only wanted to surf — we demand safe beaches."

Baja California prosecutors had said they were questioning three people in the case, two of them because they were caught with methamphetamines. Prosecutors said the two were being held pending drug charges but continue to be suspects in the case. 

A third man was arrested on charges of a crime equivalent to kidnapping, but that was before the bodies were found. It was unclear if he might face more charges.

The third suspect was believed to have directly participated in the killings. In keeping with Mexican law, prosecutors identified him by his first name, Jesús Gerardo, alias "el Kekas," a slang word that means "quesadillas," or cheese tortillas. 

Andrade Ramírez said he had a criminal record, and that more people may have been involved.

The Associated Press contributed to this report.