A school has been forced to close for the rest of the term after a former student dressed up as the Batman character, the Joker and set fire to the building, causing damage estimated at €1m.

Leaving Certificate students at Coláiste Chilliain on the Nangor Road in Clondalkin will be forced to sit their exams at other local schools following the incident, which took place last Sunday.

The 17-year-old is in custody after being arrested at the scene with a bolt cutters and three cans of petrol. It is believed that he broke into the premises with the bolt cutters, went throughout the school dousing it with petrol before setting it alight. It is believed the youth filmed the incident on his mobile phone and planned to send the footage to his friends. He did not attempt to flee from the scene and was detained by members of the fire brigade at around 3.15pm last Sunday.

When gardaí arrived to arrest him he threatened to shoot a number of officers and was taken to Clondalkin Garda Station.

Sources say that the youth was a former student at the school who was a notorious trouble maker and may have held a grudge against school management. It is thought that he was suspended on a number of occasions.

However, he had never come to the attention of gardaí before and has no criminal record.

It is thought the incident was pre-meditated and sources say that he went to bizarre lengths including putting on make-up to resemble the Joker character from the Batman films. The 17-year-old is facing serious criminal charges.

The majority of the damage was to the interior of the school with most of the classrooms destroyed beyond use.

Garda sources say that €1m worth of damage was caused and the building is in such a state that classes will not be able to resume until September.

In a statement, acting principal Caoimhín Ó Dochartaigh said the school community was devastated at the events.

"The building has sustained very substantial damage and as a result part of the school will be unusable for the remainder of the school year," he said.

However, he declined to comment on the details of the fire due to an ongoing garda investigation.

"At this time our main concern is the welfare of our students," he said, adding that alternative arrangements were being made regarding upcoming examinations.