MEXICO CITY -- Thieves apparently killed two Australians and an American on a surfing trip to Mexico in order to steal their truck because they wanted the tires, authorities said Sunday.

Baja California state prosecutors released grisly details of the slayings, but have not yet officially confirmed the identification of the bodies. They said family members of the victims are viewing the bodies to see if they can be identified by sight.

The corpses were decomposing after the thieves dumped them into a remote well about 50 feet (15 metres) deep, some four miles (six kilometres) from where the foreigners were killed. If relatives can't identify the bodies, further tests will be conducted. The well also contained a fourth cadaver that had been there much longer.

"The probability that it's them is very high," said chief state prosecutor Maria Elena Andrade Ramirez, noting the corpses 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."

The three men were on a camping and surfing trip along a stretch of coast south of the city of Ensenada, posting idyllic photos on social media of waves and isolated beaches, before they went missing last weekend.

But Andrade Ramirez described what likely would have been moments of terror that ended the trip for brothers Jake and Callum Robinson from Australia and American Jack Carter Rhoad.

She 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 well they apparently were familiar with. 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 Ramirez said.

The thieves allegedly covered the well with boards. "It was literally almost impossible to find it," Andrade Ramirez 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 Tomas was near the remote seaside area where the missing men's tents and truck were found Thursday along the coast. From their last photo posts, the trip looked perfect. But even experienced local expats are questioning whether it is safe to camp along the largely deserted coast anymore.

The moderator of the local Talk Baja internet forum, who has lived in the area for almost two decades, wrote in an editorial Saturday that "the reality is, the dangers of travelling to and camping in remote areas are outweighing the benefits anymore."

But in a way, adventure was key to the victims' lifestyle.

Callum Robinson's Instagram account contained the following slogan: "If you're not living on the edge, you're taking up too much room."

At the news conference, Andrade Ramirez was questioned by one reporter who expressed approval that such a massive and rapid search was mounted for the foreigners, but asked why, when local people disappear in the area, little is often done for weeks, months, or years.

"Do you have to be a foreigner in Baja California in order for there to be an investigation if something happens to you?' asked the reporter, who did not identify herself by name. "Every investigation is different," Andrade Ramirez replied.

As if to underscore that point, 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."

Gabriela Acosta, a surfer, attended the protest "to show love, solidarity and respect for the three lives that were lost." Acosta said that surfers in Baja are aware of the dangers.

"We are women and we would sometimes like to surf alone," Acosta said. "But we never do that, because of the situation. We always have to go accompanied."

"I think that what happened to them is just an example of the lack of safety in this state," she said.

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, Jesus Gerardo, alias "el Kekas," a slang word that means "quesadillas," or cheese tortillas. Andrade Ramirez said he had a criminal record, and that more people may have been involved.

Last week, the mother of the missing Australians, Debra Robinson, posted on a local community Facebook page, appealing for help in finding her sons. Robinson said Callum and Jake had not been heard from since April 27. They had booked accommodation in the city of Rosarito, not far from Ensenada.

Robinson said Callum was diabetic. She also mentioned that the American who was with them was named Jack Carter Rhoad, but the U.S. Embassy in Mexico City did not immediately confirm that. The U.S. State Department said it was aware of reports of a U.S. citizen missing in Baja, but gave no further details.

In 2015, two Australian surfers, Adam Coleman and Dean Lucas, were killed in western Sinaloa state, across the Gulf of California -- also known as the Sea of Cortez -- from the Baja peninsula. Authorities said they were victims of highway bandits. Three suspects were arrested in that case.