A dying man has been identified as the figure who implicated Michael Dwyer in the alleged plot to murder Bolivian president Evo Morales.
The terminally-ill taxi driver secretly filmed the conversation between Dwyer and alleged co-conspirators which triggered the fatal police raid that claimed the Irishman's life.
Although the audio from the mobile phone footage is muffled and mostly inaudible, Bolivian prosecutors claim it showed the men discussing explosives and a plot to blow up a boat carrying President Morales.
The revelation came as a Bolivian official investigating the police shooting of Mr Dwyer and two other men described the killings as sinister and said there appeared to have been what he described as a direct execution.
Mr Dwyer, alleged plot leader Eduardo Rozsa Flores (49) and another man were shot dead at a hotel in the eastern Bolivian city of Santa Cruz on April 16 in what police described as a shootout.
However, investigator Pablo Benegas said it was suspicious that no windows were shattered by the gunfire.
Bolivian authorities claim Mr Dwyer, a former engineering student from Co Tipperary, was a paid mercenary linked to right-wing separatists.
The footage obtained from the taxi driver formed key evidence Bolivian authorities put forward to justify the SWAT-style attack.
The unnamed cab driver is said to be suffering from an advanced stage of terminal diabetes. He is reported to have been hired by Mr Flores to drive him and his entourage around Santa Cruz.
According to reports, he was due to give evidence to a judge on Thursday, only for the testimony to be postponed.
Bolivian officials have also released photographs showing a bare-chested Mr Dwyer, who said he was working in Bolivia as a bodyguard for Mr Flores, brandishing semi-automatic pistols.
Mr Dwyer was buried following a funeral ceremony in Terryglass, Co Tipperary on Thursday.
Both his family and the woman he was dating in Bolivia, Brazilian medical student Rafaella Cotrin, dispute claims he was a mercenary or a terrorist.