Authorities did not provide any further details or the identity of the man.
The Robinson brothers disappeared with their US friend, Jack Carter Rhoad, during a surfing trip in the Baja California on April 27.
The siblings, aged 32 and 31, were found weeks later near their remote campsite and three Mexicans were soon arrested.
It’s believed the brothers were shot dead in a “robbery gone wrong”.
Two of those arrested were caught with meth and one of them, a woman, had a victims’ mobile phone on her.
Attorney General Maria Elena Andrade Ramírez said it is believed the brothers and Rhoad had been killed during an opportunistic robbery attempt.
But the execution-style killings raised suspicions there could be links to organised crime.
Their parents, Debra and Martin Robinson, reflected on who their sons were before their lives were heartbreakingly cut short.
“Callum and Jake meant so much to us and it’s still hard to imagine life without them,” Debra said at the memorial service.
“They were intelligent, respectful men and they had so much more to offer the world.
“They loved life and they followed their dreams.”
