Real IRA (RIRA) member Ciaran Doherty was shot dead by members of the same organization.
The RIRA suspected Doherty of supplying information about a cannabis factory in County Donegal to the police. The police raided the drug factory last month.
The RIRA has claimed responsibility for murdering Doherty. The father-of-one's semi naked body was discovered on the outskirts of Donegal with his hands tied and gun shot wounds to his head and chest.
The RIRA issued a statement saying: "We executed him because he was involved with a criminal organization with links to the drugs trade and was profiteering. He knew the risks involved in what he was doing."
RIRA member Seamus McCreevy, who was found dead in his home in County Meath last week, owns the house that was used in the growing of marijuana.
However, the police have ruled out foul play in his death.
Currently there is no evidence to connect McCreevy to the marijuana grow house.
Doherty was never a member of a republican group until he joined the RIRA during the Provisional IRA ceasefire. Doherty had met McCreevy in jail while serving a custodial sentence in Portlaoise Prison.
Doherty was subsequently jailed again for the armed robbery of a Donegal nightclub in 2002.
Doherty had told the Derry Journal last year that the British intelligence agency MI5 tried to recruit him as an informant when was caught trying to set up an illegal cigarette factory by MI5 and customs officials.
The Police Service Northern Ireland (PSNI) searched his house for drugs in January. Doherty then released a statement in the Derry Journal and denied he had any involvement in the drugs trade.
Doherty was due to be married in three months to the mother of his two-year-old daughter.