Authorities previously claimed the Polish and German cyclists, whose bodies had been found at the bottom of a ravine in Mexico, had died in an accident.
Investigators examining the deaths of two European cyclists in the southern Mexican state of Chiapas now say they were murdered.
The bodies of Polish man Krzysztof Chmielewski, and Holger Hagenbusch from Germany, were found on April 26 and May 4 in a 200m-deep ravine after they were reported missing by relatives. Only one bicycle was also recovered.
The pair met in the tourist town of San Cristobal de las Casas on April 20 and planned to cycle to the ancient Mayan ruins at Palenque about 200km away when they disappeared, according to investigators.
Authorities first suggested that they died after losing control of their bicycles on a winding road and had plunged down a cliff. But fellow cyclists questioned their theory as one of the men had been decapitated and was missing a foot, while the other appeared to have been shot in the head.
A newly appointed special prosecutor now says the men were murdered.
"It may have been an assault, because our investigations up to now indicate this was an intentional homicide," Luis Alberto Sanchez told reporters.
He added that the motive may have been robbery.
The Chiapas government has meanwhile said they will “intensify the investigation” to solve the case.
It comes just weeks after 25 German tourists and three Mexicans were robbed on a bus by armed men while travelling to Palenque on March 31.
The ancient city, which dates back to around 100BC, is a tourist hotspot which attracts hundreds of thousands of tourists every year.