The mother of an Irish security worker shot dead by Bolivian special forces has said she has further evidence that her son was an innocent victim.

Michael Dwyer, 24, from Brocka, Ballinderry, Co Tipperary, was killed in April 2009 over an alleged political assassination plot targeting president Evo Morales.

His mother Caroline spent time in Bolivia pressing for support for an independent investigation into the shooting of her son, whose body was found at the Las Americas Hotel in Santa Cruz.

She said she visited the hotel where her son died, met representatives from the Bolivian government and witnesses in the case surrounding her son's killing.

Ms Dwyer said: "Everything I saw and heard is further evidence that Michael was an innocent victim and was unlawfully killed.

"It is essential that his name is cleared and a proper investigation is conducted into his killing."

The Dwyer family complained to the United Nations' special rapporteur on extra-judicial killings last November after receiving new information on the killing.

They were given photographs of Mr Dwyer at an airport on the day he was killed.

Marcelo Soza, the former Bolivian chief prosecutor who is seeking refugee status in Brazil following the killing, told the family last summer that he believed Mr Dwyer was unarmed when killed. 

Post-mortem reports have also indicated that Mr Dwyer was unarmed.

Mr Soza claimed there was no shootout in the hotel, as initially alleged, and no evidence that Mr Dwyer was knowingly involved in an assassination plot.

He said he was appointed to investigate the case days before the killing.

Mr Dwyer was employed by I-RMS on Shell's Corrib gas project in Co Mayo before travelling to Bolivia for further training as a bodyguard.

Hungarian Elod Toaso, who was with him before his death, told a trial into his involvement in terrorism that the Irishman survived the hotel raid at Santa Cruz in April 2009 - where it was reported he had been shot - and was later seen alive at the city's international airport.

He claimed Mr Dwyer was probably summarily executed at Viru Viru airport.