This arrest was another staging post in a long campaign by gardai to convict O'Reilly in what is often called the "court of public opinion". In this campaign they have succeeded spectacularly. There can hardly be a person in the country who, from the mass of innuendo, leaks, misinformation and disinformation which has appeared in various organs, has not developed an opinion about O'Reilly's guilt. I would wager that almost all of those people have come to the same conclusion: Joe O'Reilly killed his wife.

And, although this is hardly the point, they may well be right. The point, rather, is that when a murder is committed, gardai are supposed to conduct their investigations, eliminate suspects from their enquiries, gather evidence against the person they believe did it, present that evidence in court before a judge and jury, and hopefully secure a guilty verdict. In giving that verdict, the jury will have considered only evidence put before it in court.

This is not what is happening in the investigation into the death of Rachel O'Reilly. In this case, gardai believe that Joe O'Reilly killed his wife (O'Reilly himself acknowledges he is a suspect), but because they have so far been manifestly unsuccessful in proving this, or even in building up enough evidence to persuade the DPP to go anywhere near a courtroom, somebody within the force has organised a kind of public lynching instead.

Over the last 18 months, this has involved a series of leaks about mysterious new evidence which would put the Number One Suspect away.

The result has been a kind of drip-feed effect in which the guilt of Joe O'Reilly (aka the Number One Suspect) is insinuated into the public consciousness to the point where almost everybody purports to know or believe that he killed his wife. It's guilt by a thousand leaks.

If O'Reilly is ever charged with murder, the jury will have to be chosen from a population which has been bombarded with those leaks and innuendoes. The 12 men and women will come to court, therefore, having been invited many times previously to consider the guilt or innocence of Joe O'Reilly, and to come to the conclusion, as the gardai leaking to the newspapers have done, that the defendant is guilty.

In that circumstance, lawyers for O'Reilly would spend the first few days of any court case arguing that there was no possibility that their client could get a fair trial, his guilt having already been hinted at over a long period of time in dozens upon dozens of newspaper stories. Therefore, they will say, there should be no trial at all.

Of course, the judge could well decide that this is nonsense and that the members of the jury will be able to rid themselves of whatever prejudices they have. Throughout the history of the Irish courts, judges have been consistently resistant to the notion that juries can be prejudiced by media coverage.

However, throughout the history of the Irish courts, there has never been a situation in which a potential defendant in a murder trial has been so consistently hounded by a combination of newspapers and their garda sources. The judge could well decide, therefore, that Joe O'Reilly cannot get a fair trial, that jury members will not be able to rid themselves of whatever prejudices they bring with them.

That gardai may never catch the killer of Rachel O'Reilly is an appalling enough prospect, but that they would put the trial of a potential defendant at risk by a campaign of smears, leaks and tip-offs about arrests, is truly shocking, exactly the kind of thing you'd expect somebody like Michael McDowell, the justice minister, to get worked up about. This is a man, after all, who loves to boast about his commitment to the rule of law. What could be more offensive to such an individual than to see such a potentially important and high-profile murder trial put at risk by the very force assigned to make it happen?

The problem for McDowell is that he has been engaged in precisely the same kind of campaign of leaking and innuendo against people he believes to be guilty of crime. In the case of Frank Connolly, the then head of the Centre of Public Inquiry, he handed over garda documents to his buddy, the journalist Sam Smyth, who wrote a story about Connolly applying for a false passport. McDowell then used Dail privilege to accuse Connolly of other illegalities. Like the gardai who leak to the media about Joe O'Reilly's guilt, McDowell never provided any evidence for his claims.

On Ursula Halligan's TV3 show last weekend, and in the current issue of Village magazine, businessman Phil Flynn suggested that McDowell had tried to criminalise him through a "concerted media campaign" which involved the briefing of certain journalists. Amongst stories which appeared, although Flynn did not refer specifically to it, was one written by Sam Smyth in February of last year. It claimed that Flynn was "linked to a Cork-based finance company at the centre of the investigation" into alleged money laundering.

Last month, however, the Irish Times reported that Flynn had not featured in a garda file sent to the DPP on the investigation. The man who 12 months earlier had been at the "centre" of an inquiry turned out to be entirely innocent.

McDowell's willingness to leak against people who displease him makes him the moral guide and guardian angel of the gardai who have been leaking about Joe O'Reilly. If he will not stop doing it himself, we cannot expect that he will ask gardai to stop.

Should, therefore, any future trial of O'Reilly collapse because of the campaign against him, McDowell will not be able to shirk his responsibility.