© PA WireKieran Doherty, who was murdered by British intelligence agents in Co. Derry last year.
That is despite the British government's security adviser deciding MI5 had no connection to the Derry death of Kieran Doherty (31). No inappropriate or improper action took place, Lord Carlile added.
Mr Doherty's body was discovered on the outskirts of the city close to the Border in February 2010. He had been shot dead. The Real IRA said he had been killed because of links to the drugs trade.
Mr Doherty's uncle Vincent Coyle said: "There is a case now for the Police Service of Northern Ireland (PSNI) to carry out an investigation into this."
He added: "The security services seem to be left doing their own thing. The old Royal Ulster Constabulary Special Branch took huge pay offs on the Monday and were back as MI5 officers on the Tuesday."
Lord Carlile spent four months investigating the family's claims MI5 were involved in the killing and met relatives. He sent a letter to SDLP Foyle MP Mark Durkan.
He said his conclusions must be broad because of potential national security issues. "My conclusions are clear. No inappropriate or improper action took place. Kieran Doherty's cruel death was not in any respect a consequence of any misbehaviour or infraction by anybody directly or indirectly connected with the public service," the letter said.
"Further, the PSNI have been able to carry out a full and unimpeded murder inquiry."
Mr Coyle said the conclusion that the PSNI had not been impeded in their murder investigation left an avenue open for further investigation. He called on PSNI chief constable Matt Baggott to carry out a probe into the allegations made against MI5 by the the family.
Lord Carlile is an independent government adviser on the activities of the security services and met the family of Mr Doherty in Derry last year.
In the months before he was killed, Mr Doherty told a local newspaper MI5 had tried to recruit him as an agent.
The Real IRA said it murdered the victim - a senior member of their organisation - over alleged involvement in drugs. But his family claimed MI5 was involved.
Lord Carlile pledged to investigate the family's allegations and report back to Northern Ireland Secretary Owen Paterson.
Since when has any member of the club found fault within their own club membership? Perhaps there is an exception to prove the rule, but with the overwhelming vast majority of 'investigations' finding the PTB are never wrong, why should anyone expect differently? I did like the funny part about him being "an independent government advisor on the activities of the security services". Who says the Brits don't have a lovely sense of humor?