It is understood detectives believe Guerin's movements were passed from a suspect to two men thought to have shot her on 26 June as she waited at traffic lights on the outskirts of the city. In turn, sources believe information may have come from a police officer in the pay of the crime boss.
Suspicions about police involvement have arisen as the number of officers caught up in the investigation reached as many as 15. None has been directly linked with the murder, but sources say they have come under investigation as off-shoots of the main inquiry.
So far, detectives have arrested more than 100 people, with another five detained yesterday, in connection with their inquiries, more than 100 firearms have been seized, 230 properties have been searched and a variety of drugs have been impounded.
According to one politician, pounds 600,000 in used banknotes was seized last week from the homes of suspects who may have been shielded by corrupt officers. The Garda said yesterday that the figure was nearer pounds 100,000.
Guerin, who worked for the Sunday Independent was shot in her car while at traffic lights after appearing at Naas District Court on a speeding charge. It is understood detectives are concerned that details of that appearance may have been passed to the crime boss by an officer in his pay.
One source with close links to the security services said: "Who else would have known she was going there? Her husband perhaps, or a friend or work colleague. Certainly it is no coincidence that the assassins knew where to wait."
A man appeared in court last week in connection with the killing. Paul Ward, 32, was charged with conspiracy to murder her and with harbouring her killers. It is understood the police have identified two main suspects, who are on the run.
But the investigation has uncovered widespread concerns over the probity of some officers. A senior Dublin politician, who asked not to be named, said: "During the trawl of all the people who were arrested, more information came to light, mainly involving claims that Gardai were consorting with, or were in the pay of, criminals."
Sources say there is evidence that a number of officers received payments of around pounds 500 a week in return for turning a blind eye to the activities of drug dealers. Next week, at a public meeting on the outskirts of Dublin, concerned parents are understood to be considering naming two local officers they believe have been taking bribes or "shaking down" small-time dealers for their drugs and profits.
"People are sick of it," said one source. "They would find some guy selling ecstasy to their kids and give him a good hiding, only to find out that they were the ones in trouble with the police. Now they think they know why."
Last week John O'Neill, 32, a police officer decorated two years ago for bravery, resigned after being charged with accepting a pounds 200 gift or bribe, the illegal possession of a sawn-off shotgun and conspiring to pervert the course of justice by destroying an arrest warrant.
There have been other reports of detectives being questioned over links with a suspect in the Guerin case and of one officer receiving pounds 3,000 for signing passport forms for gang members.
And two weeks ago in Cork an investigation was ordered following evidence that some officers had been consorting with criminals.Reuse content