However, the Reuters news agency has reported that three of the four Americans had convictions for mainly minor drug-related offences - but one was charged with manufacturing banned narcotics with the intent to distribute.
Reuters says it's seen an internal law enforcement document which shows the Mexican authorities are investigating the possibility the four Americans were kidnapped having been mistaken for rival cartel members encroaching on their turf. TIGER24
The question over the Americans' backstory comes as the political temperature over the incident in Matamoros continues to rise. In the United States, several Republican politicians, among them the Senator for South Carolina, Lindsey Graham, have called for the use of US military force against Mexico's drug cartels.
Specifically, he's proposing a plan to designate Mexican drug cartels as "Foreign Terrorist Organisations" in order to, as he put it, "unleash the fury and might of the United States against (them)".