Investigators in Mexico have returned to the scene where two Australian brothers and a US national were killed during a suspected “robbery gone wrong”.
Three Mexican locals were arrested over the weekend after the bodies of Callum and Jake Robinson and friend Jack Carter Rhoad were discovered 10 metres down a well.
Authorities told 9News’ Alison Piotrowski they had not ruled out the involvement of further suspects.
A convoy of 20 army vehicles pulled up to the campsite on Monday (Tuesday AEST) in Baja California where the three men were last seen on April 27.
Forensic investigators were seen combing a remote dirt track for evidence as Mexico’s National Guard scoured the above cliffs.
Police said they were unable to rule out any additional suspects as they were still collecting evidence and the investigation was ongoing.
Two of the arrested trio were caught with methamphetamines. One of them, a woman, had one of the victims’ cellphones when she was caught. Prosecutors earlier said the two were being held pending drug charges but continued to be suspects in the killings.
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 Attorney General Maria Elena Andrade RamÃrez said it was believed the brothers and their friend had been killed during an opportunistic robbery attempt.
But the execution-style killings had locals asking whether there could be links to organised crime.
Jake and Callum’s parents, Debra and Martin, travelled from Perth to Mexico to identify their bodies before crossing the border into the United States.
A GoFundMe page has been launched to cover travel and accommodation and funeral costs while an investigation is under way.
The fundraiser had already raised US$250,000 ($378,788) out of its $300,000 ($454,545) goal by Tuesday evening.
A vigil was held for the three men in Callum’s adopted hometown of San Diego. 
“Cal Robinson was just bigger than life,” friend Peter Green said.
“An absolute legend, a guy that lit up the room. He had his own gravitational pull.”
