IT BEGAN as little more than a simple prank, a guerrilla statement of artistic intent. Conor Casby walked through the front door of the National Gallery with a satchel on his back, one of thousands of other visitors to the august institution that fine Saturday afternoon, 7 March.

The Mayo artist was calmness personified. His portrait of Brian Cowen had been painted two months earlier and Casby had already carefully selected a spot in which to hang it, preparing a detailed caption to sit alongside it.

The by-now infamous image of Taoiseach Brian Cowen, seated on a throne with a roll of toilet paper in his hand, took pride of place alongside a picture of Maeve Binchy in the hallowed halls of the portrait gallery.

Undaunted by the experience, Casby repeated the experiment the following day at the Royal Hibernian Academy on Ely Place, where he hung a second unflattering picture of the country's premier, this time holding a pair of blue underpants.

On both occasions, he was accompanied by a friend, who took pictures of the Cowen portraits as onlookers passed by, convinced the paintings were simply part of the collection.

The following day, the Sunday Tribune was contacted by a source at the National Gallery. The painting had hung for close to an hour, we were told. The portrait had been removed and the National Gallery contacted officers at Pearse Street garda station, standard practice when any possible breach of security has taken place. Even the gardaí were bemused when they arrived, telling staff that no offence had been committed because the renegade artist had not interfered with the gallery's priceless art collection.

The source was able to provide a mobile-phone picture of both the portrait and the prankster painter. The Sunday Tribune made contact with the National Gallery.

Clearly embarrassed, it released a short statement explaining that "an unauthorised item" had been put on display.

"One can only surmise that it was an action by someone seeking to use the gallery for self-promotion or other reasons. Incidents that are in breach of the day-to-day operations, and with possible implications for security of the gallery, are routinely brought to the attention of the gardaí," it said.

Naked

Meanwhile, Conor Casby had also determined that his efforts would not be in vain. The Sunday Tribune had previously reported on another naked portrait the Claremorris man had painted, of former taoiseach Bertie Ahern.

Using the pseudonym Topsy Campbell, he emailed copies of his new picture to this newspaper with a simple explanation: "Please find attached details of temporary exhibitions that took place in the RHA and the National Gallery between 2.30pm on Saturday March 7 and approximately 11am on Sunday March 8."

Casby – whose exact identity at that stage remained a mystery – was not interested in further explanation, however, writing an email that simply said: "I would much prefer not going public if that's at all possible."

Last week, the Sunday Tribune published the pictures, setting in train a scarcely believable set of events, which culminated in a grovelling apology from RTé and a bizarre garda investigation that almost ended in a raid on the offices of radio station Today FM.

Ironically, the story had already appeared to have reached the end of its natural life last Monday before the ill-advised intervention of the Government Press Office.

As almost always happens on a quiet Sunday afternoon, the original story had been rewritten by most of the tabloid newspapers for their Monday morning editions and studiously ignored by the broadsheet papers.

Meanwhile, Ray D'Arcy on Today FM revealed that his show had also been emailed the pictures by a friend of Casby, and it contacted the artist live on the air. At first he denied any involvement but later admitted that he was the one responsible.

Even still, the story was on the verge of extinction, and the picture destined to become one of those mildly amusing images that fill up thousands of people's email inboxes every day.

Or so, at least, it seemed – until a seemingly innocuous report on RTé's Nine O'Clock News featured the paintings story once more.

It was a short report, just 96 seconds in duration, delivered by reporter Tadhg Enright in that unique broadcast style reserved for those 'and finally' items.

Infuriated

The government press officer Eoghan Ó Neachtain was infuriated by the tone of the piece. He placed a direct call to RTé director general Cathal Goan and they talked for a few minutes, speaking in Irish.

RTé agreed to make an apology, even though no similar complaint had been made to the Sunday Tribune, which bore ultimate responsibility for the images having becoming public in the first place.

Ó Neachtain, a former commandant in the Defence Forces, insisted that he had acted under his own steam: "I made the call myself and not at the request of the Taoiseach."

RTé said there had been no demand for an apology but clearly felt it had erred, and the offending item was quickly removed from its website.

A spokeswoman said: "The first thing to state is that it was an RTé decision. The newsroom decided after the bulletin went out that the item was in bad taste. It was our decision that it wouldn't be broadcast in subsequent bulletins. News on Two would have been the most immediate, and the decision was taken immediately not to broadcast it on that show, and it was immediately taken off the internet, because it was just in bad taste.

"Subsequently, we did receive complaints, including one from the Taoiseach's office, but it was our decision to take it down before we got the complaints, which were understandable."

By Tuesday, Fianna Fáil TD Michael Kennedy was calling on RTé 's director general to "consider his position", while the national broadcaster made arrangements to broadcast its apology.

Newsreader Eileen Dunne ended Tuesday night's bulletin saying: "On last night's programme, we carried a report on the illicit hanging of caricatures of the Taoiseach in two Dublin galleries. RTé News would like to apologise for any personal offence caused to Mr Cowen or his family and for any disrespect shown to the office of the Taoiseach by our broadcast."

Once RTé apologised, the story gathered serious legs. It featured on the front pages of most national newspapers, and papers across the world also picked up on the story.

Dust

The garda file on the paintings had all the while been gathering dust in the bottom of a filing cabinet somewhere in the bowels of Pearse Street garda station.

On the day that the painting was hung in the National Gallery, gardaí had been provided with a clear CCTV image of the painter. A few routine checks with galleries around Dublin would surely have yielded the identity of the renegade artist.

But two weeks had since elapsed and absolutely no attempt had been made to track down the artist.

It was only the Taoiseach's ire which at last provoked some response from the gardaí, and a plainclothes detective arrived at the studios of Today FM on Tuesday morning. He demanded access to the station's email system and told the programme's producer Will Hanafin that "the powers that be want action taken".

Casby – a schoolteacher in Dublin's north inner city – was finally under real investigation on suspicion of three offences, namely: incitement, indecency and criminal damage [for hammering a nail into the wall of the National Gallery].

The artist was by now overwhelmed by the farrago that had developed. He made contact with the Sunday Tribune: "The reason I didn't get back to you today was that I was trying to concentrate on work because on Monday my head was fried with the developments and I got nothing done at work. Didn't get much done today either so tomorrow there'll be more pressure to catch up. Also, the gardaí became involved today so I have another issue to wrap my head around."

Casby had voluntarily gone to Pearse Street garda station, where he was questioned by detectives.

He admitted that he was responsible for the paintings and, in his anxiety to co-operate, produced other nude paintings of Brian Cowen and also of former justice minister Michael McDowell.

In an email, he said: "In terms of talking you through the whole process, I have already spoken to the gardaí and would prefer not to comment. In terms of the arguments going on in the media now, I think they're less and less to do with me. As much as I can say about it is that it's interesting for me to see things like this develop through the media from a viewpoint other than that of punter. But... I think my involvement is vicarious.

"In terms of the piece itself, I took an image from one medium, the newspaper, and transplanted it to another, portraiture. Both of these media are largely controlled by those represented in them and the project I undertook in painting the picture was to illustrate this point.

"The pictures were really meant more as a comment on the use of media than an attempt to use the media to comment. The anonymity and the profitless nature of the project was central to this.

"From my perspective, I would like to draw an end to this by offering the portraits to the highest bidder and donate the proceeds to charity. I'll see if I can organise that."

Embarrassment

Later on, Casby said he had been all but exonerated by gardaí and, certainly, the investigation at Pearse Street appears to have halted amidst crushing embarrassment for garda management.

No attempt has yet been made to obtain emails from the Sunday Tribune and Casby said: "I've been told that it is over and done with as far as they are concerned."

On the internet, thousands of email petitions, Twitter messages and Facebook groups emerged whilst dozens of other unflattering portraits of Brian Cowen appeared online.

The original Sunday Tribune story spawned dozens of comments on our website, almost all in support of Casby, while international media outlets including the New York Times, the Guardian and the BBC reported on what was turning into another typically Irish controversy.

RTé broadcaster Pat Kenny also rallied to the Casby cause, saying: "I would want to buy the picture and hang it on my wall at home, because I have a sense of humour."

Casby meanwhile attempted to drift back to the anonymity of his everyday life, bewildered at how a Saturday afternoon prank had given him so much more than his 15 minutes of fame.