Investigating the murder of a Limerick nightclub security man, Mr Brian Fitzgerald, could be more difficult if the killer was an outside "professional", the Dáil was told.

The Minister of State for Justice, Mr Willie O'Dea, said no stone would be left unturned in the inquiry and no murder in the city in the past decade remained unsolved.

Mr Fitzgerald (34), head of security at a Limerick nightclub, was shot dead in November, having thwarted a gang trying to sell drugs in the club.

The Garda and "the people of Limerick, including myself, have a strong suspicion of who is involved in this murder", but they could not act on the basis of suspicion, Mr O'Dea said.

"The difficulty that confronts the investigation so far is that there are two possibilities. Either a particular crime family or some of their associates carried out the killing or they brought in a professional from the outside."

The Minister, who is also TD for Limerick East, said if it was an outsider "there would be no connection between the victim and the perpetrator and that makes the investigation all the more difficult".

Mr Dan Neville (FG, Limerick West) had asked what message was being given by this "dastardly act". He said everyone in Limerick knew who was responsible.

"They are frightening those who want to protect young people, who do not want to have drugs pedalled on their premises and who want to run decent places."

The signal had been given, he said, "that if you protect children, do your job and do not allow drugs in, or even if you speak about them, your life is in danger.

"What message does that give to people in similar positions, even owners of nightclubs?"

The murder was like that of journalist Veronica Guerin and in that case "the drug barons of Dublin were routed out and brought to justice. I ask the State to respond in the same way to the death of Brian Fitzgerald," Mr Neville said.

The Minister assured the Dáil that while the Government normally adopts a "hands-off" approach to Garda investigations, "I am keeping in touch with the Garda about the progress of this investigation". He added: "I have assured them that if they need any assistance, equipment, back-up or people from the outside, they need only telephone me and I will make them available."

Mr O'Dea said he had the agreement of the Minister for Justice and the Garda Commissioner on that.

Mr Neville said Mr Fitzgerald had made a statement to the Garda about criminal activity "and had a gun put to his head to make him withdraw it.

"Following advice, although he did not want to, he withdrew it for the safety of his family and still he was killed.

"He abhorred drugs."

Mr Neville raised Mr Fitzgerald's murder during the debate on the Private Security Services Bill, which will regulate the security industry including "bouncers".

The legislation, which goes to committee stage next, creates an authority which will control and supervise people providing security services.

The authority will also have responsibility for the licensing of companies and every individual in the security industry, Mr O'Dea told the House.