Perth brothers Callum and Jake Robinson went for a quick surf weekend in Mexico. How did it go so wrong?

By North America correspondent Carrington Clarke in Ensenada, Mexico and Rebecca Armitage, ABC

It was meant to be an idyllic surf adventure down Mexico's north-west coast.

Australian doctor Jake Robinson, 30, flew over to San Diego, where his older brother Callum was based.

Both athletic, outdoorsy adventurers who shared a love of the waves and adventure, they decided to grab a friend - American Jack Carter Rhoad - and head south for a quick surf jaunt.

Like so many before them, they were lured by Baja California's crisp, sparkling waves, as well as the chance to camp on rugged and remote beaches among the wildflowers.

Here, beaches are often referred to by their latitude and in late April, the men visited the K38 surf break.

Rodrigo Leal Bravo from the local surf shop remembers them coming in to buy wax.

"They were excited about their surf trip and they were on their way south," he told the ABC.

He noticed the strong bond between the Australian brothers.

"Their fraternity was so admirable," he said.

Callum told Rodrigo they were heading to Punta San Jose, a remote spot which was about three hours drive from the surf shop.

It's only accessible by unsealed roads and the mobile tower coverage is patchy at best, but Rodrigo says he wasn't concerned for their safety.

"I did not think anything should happen to those big strong guys, right?" he said.

But when Callum didn't show up to work in San Diego after the weekend, loved ones were confused, then concerned, and then finally panicked.

Three bodies have been found where Callum, Jake and Jack went missing - though they are yet to be formally identified.

"All three bodies meet the characteristics to assume with a high degree of probability that they are the American [Jack] Carter Rhoad as well as the Robinson brothers from Australia," said Baja California's state Attorney-General María Elena Andrade Ramírez.

Mexican authorities have also detained two men and a woman in connection with their disappearance.

As the case is investigated, a devastating picture is emerging of what may have gone wrong on the scrubby cliffs overlooking the Pacific Ocean.

A weekend jaunt south of the border

Callum shared glimpses of their Mexican surf trip on his Instagram account.

The first photo shows their white Chevvy packed with boards and towels right near the water's edge.

"....and it begins," Callum wrote as the caption, along with a surfer emoji and a picture of the Mexican flag.

He then added more snapshots of their journey - taco stands, brightly coloured buildings, and Jack beaming with a boom box on his shoulder.

The stories ended abruptly with a picture of Playa San Miguel, a crop of yellow daisies growing at the edge of the sand.

They were reported missing about two days later, but in Baja California, timelines can be difficult to piece together.

As each wave crests and breaks, as each taco is procured from a local food stand, and as each sunset melts over the Pacific, the days start to blend.

Locals and tourists alike have vague memories of seeing a pair of Australian brothers and their American friend riding the waves on the northern Mexican coast in late April, but exact dates are difficult.

Callum, a 190-centimetre-tall athlete with cascading brown hair, turned heads everywhere he went.

"I remember seeing one guy that ... could have been like, a rugby player or division one football player," visiting American surfer Austin Pickle told the ABC.

"They were smiling and you know, doing like the friendly surfer [chatty] thing. But yeah, nothing super strange.

"And then I just paddled in. I never saw them again."

Ana Cristina Heym Cárdenas works in a cafe about an hour north of Punta San Jose.

She believes one of the men - probably Callum - came in the afternoon of April 28 to ask if she could break a 100-peso note so he could buy a taco from the stand outside.

She was shocked to later hear that they disappeared.

"It's not normal here - [the] disappearing of three people in this way and burning their car and all this," she said.

"We know that some areas here in Baja California, they're dangerous.

"We feel very sad because there are good people here [in Baja] who like international tourists. We don't want other people thinking that it is too dangerous for people."

A gun, a burned-out car and a missing phone

It's every parent's dream for their children to stay close in adulthood.

But Debra Robinson sensed something was wrong when her sons stopped picking up their phones during their holiday together in northern Mexico.

In late April, she got on a Baja Facebook group, posted a picture of her boys together and issued a plea.

"They were due to book into an Airbnb in Rosarito after their camping weekend but they did not show up," Robinson posted.

While others in the group tried to reassure her, reminding her that mobile reception in the area is patchy and roads are often unreliable, she insisted their disappearance was "out of character".

"Callum is a type one diabetic so there is also a medical concern. Please contact me if you have seen them or know their whereabouts," she wrote.

"Please please please."

Callum, Jake and Jack were soon reported missing, and Robinson marshalled foreign agencies and police to search for her sons.

While Baja California is plagued by drug cartels, crimes against foreign tourists are relatively rare, and well-populated areas are considered more safe.

"It is an atypical, exceptional case," Attorney-General María Elena Andrade Ramírez told the ABC.

"We have a tourist influx and a similar case has not occurred."

On Saturday, it was confirmed that three bodies have been discovered in what's described as a well close to where the men were last seen.

Forensic investigations are continuing to take place to formally identify them.

The details are not yet known, but at some point, Jake, Jack and Callum were separated from their belongings - including their Chevy, their tents and at least one of their phones.

This week, that phone was traced to a 23-year-old Mexican woman, who has since been arrested.

Her romantic partner and his brother have also been detained, and Andrade Ramírez says they "may be directly or indirectly related to the investigation".

All three suspects were allegedly in possession of illicit drugs, but this incident does not seem to be linked to organised crime.

Another key part of the investigation is likely the remote ranch where the brothers' burned-out car was found.

The property is several kilometres from the initial search site and is located south of the city of Ensenada.

"We have secured a cell phone and a firearm," Andrade Ramírez said.

"The firearm was discovered in the pick-up truck belonging to an individual currently under investigation.

"A criminal scene has already been processed where we found evidence that someone burned the remains of tents, clothes, drink bottles and some evidence related to this case."

At this stage, investigators are treating this as a potential robbery gone wrong, with the suspects allegedly trying to steal the victims' car.

"This aggression seems to have occurred in an unforeseen, circumstantial manner," Andrade Ramírez said.

"We pledge that this crime will not go unpunished."

'They were together doing something they passionately love'

With three bodies discovered - but yet to be identified - the Robinsons are on their way to Mexico for a task no parents should ever have to complete.

The fact that crimes against foreign surfers are exceptionally rare in Mexico is no comfort when your babies are the unlucky ones.

So far, the case appears to have eerie similarities to the slaying of two Perth-born surfers in Mexico in 2015.

Dean Lucas and Adam Coleman were on the trip of a lifetime, surfing down the Baja California coast.

But when they arrived in the badlands of Sinaloa, they were stopped, robbed and then killed by a gang.

But most surfers will tell you, chasing the best waves sometimes takes you to some dangerous places.

"[Punta San Jose] is a beautiful place with perfect waves," Antonio Otanez from the Baja Surfing Association told the ABC.

"But it's very lonely there. And it's like one hour [away down] a dust road. There's no [phone] signal there."

Otanez said the local surf community has been left devastated by the news, but no-one is hurting more than Jake, Jack and Callum's parents.

"Surfing is a passion they both share," Robinson said of her sons.

"Our only comfort right now is that they were together doing something they passionately love.

"We ask people to keep them in their thoughts and prayers."

- ABC