On Sunday morning seven weeks ago, Patrick Clancy got a knock at his front door that changed the course of his life. He was greeted by two gardaí standing on his front doorstep. Invited inside, it soon became clear they had come to deliver bad news. His son Shane's car had been discovered early that morning outside a house in Bray where a young man had been fatally stabbed and two others had been injured. The gardaí believed his son was responsible. "It was as if their words fell to the floor. I said, 'If you're looking for him, you're wasting your time.' I knew immediately that my son would not be able to inflict that on other people and still be alive; I knew he could not live with himself."

His paternal intuition was right. The 22-year-old Trinity student was lying dead in the back garden of Sebastian Creane's family home in Cuala Grove, Bray. Gardaí had yet to discover his body, but Shane had turned the knife on himself after fatally stabbing Sebastian and injuring his ex-girlfriend Jennifer Hannigan and Sebastian's older brother Dylan in a knife attack.

"It's not the Shane I know and love. He wouldn't hurt a fly. He was a pacifist. I know in my heart and soul it was Shane's hand that took a life – but it wasn't his mind. I do not know how he got to that point. He spent 22 years on this planet as a wonderful, loving person. But people are now judging him on the last hour of his life."

The gardaí asked Patrick to try and phone his son that morning but it went straight to voicemail. "I don't blame the gardaí for not finding his body immediately. I'd like to thank the two gardaí who called to my house that day for how they handled it and all the gardaí involved in the investigation. In the next few days, it was hard to take in the circumstances of what happened. It goes against everything my son stood for."

Shane's personality was light years away from what happened on that fateful night in Bray. In the seven weeks since his death, Shane's father has been trying to reconcile in his mind how the well-adjusted young man he helped raise could be capable of such mindless violence. Patrick is acutely aware of the sense of loss and pain the Creane family are experiencing as a result of his son's actions. "The last thing I want to do is upset the Creane family. Loss is loss. There are no words. I can't give them back their son, I wish I could. But I owe my son this much. I have to tell people about the type of person my son really was."

Shane had no history of mental illness and lived life to the full. He was entering in his final year at Trinity College studying Irish and Biblical and Theological studies. He lived in an apartment in Dalkey and had cousins and an uncle living nearby. He regularly saw his father, who lives in neighbouring Dun Laoghaire, and his mother Leonie, who lives in Redcross, Co Wicklow, with her second husband Tony and their three children.

Shane was a young man with a busy life. He didn't smoke or drink and had a large circle of friends and interests; he was passionate about the Irish language, keeping fit and travelling. "To describe what he did as out of character is an understatement. He was a happy, independent young man. To know him was to love him," adds his father. Patrick remembers his son as someone who was always reaching out to help others. When he was 10 or 11, his father brought Shane and his two younger brothers Liam (now 20) and Jake (now 18) to a pound shop.

"I gave each of them a pound and the three of them ran in to spend it. When the two younger boys were paying for what they bought I asked Shane what he was buying. He pointed to a homeless man outside. He'd given him the money instead of spending it on himself. That was Shane."

On his 21st birthday held in the Club in Dalkey, where he worked, Shane left a collection box for St Vincent de Paul for his guests to make a contribution rather than bring a gift. Last Christmas and the Christmas before, Shane phoned his father to say he'd be late up to visit him. "He was feeding the homeless in Stradbrook. The kind things he'd do wasn't something he'd tell people about. He'd be embarrassed if he could hear me talking about him now. He was a gentleman."

What kind of a big brother was he? "He was the best," says Liam, with a simple shrug of his shoulders. "Always there for everyone."

Feeling low

Patrick knew his son was feeling low over the break-up of his relationship with Jennifer Hannigan. Shane had ended the three-year romance but never got over it. By the time he'd decided he wanted to reconcile with Jennifer, she had moved on and had begun dating Sebastian Creane. The pair were both students at the Dun Laoghaire Institute of Art, Design and Technology. Shane was due to travel to Calcutta during the summer to do aid work but pulled out. "He told me he didn't feel up to it. He went to Thailand and Australia instead – one of his cousin's lives in Thailand so he visited him. The last time I saw him was a few days before he went. I asked him if Jen was going with him and he told me they broke up. 'Do you mind if I don't talk about it,' he said. I said 'of course'. He went to try and clear his head, to sort himself out. He was 22 and broken-hearted. When you're that age, you think it's the end of world. Himself and Jen were a lovely couple; she's a lovely girl. They were very happy whenever I saw them together. He was besotted with her and she was besotted with him," he recalls. "I think she knows what happened that night wasn't really him."

Patrick was worried enough about his son to ring his nephew in Thailand to enquire about how he was getting on. "He said Shane was still a bit down but seemed better than when he first arrived. He was reading Barack Obama's autobiography. Obama was a hero of his, so was Ché Guevara. And Superman, he loved Superman."

But when Shane returned from his trip, he was still suffering. His father didn't get a chance to see his son when he returned from his travels. During college term, Shane would call up to his dad's for dinner every Monday and Wednesday but during summertime, he'd see him less frequently

Depression

But Shane did see his mother Leonie and confided in her about how he couldn't seem to get over his depression. Then he went to the doctor with his mother. The GP prescribed Citrol, a brand of the antidepressant citalopram.

Shane was taking it for about a week when he took the remaining three weeks' supply in one day, possibly an attempt at suicide. He told his mother what had happened. Two days later, she took her son to another GP. It was explained to the second doctor that Shane had taken a high dosage of Citrol two days previously. The GP prescribed Cipramil, another brand of citalopram.

As this GP was aware Shane had misused antidepressants two days previously, it was instructed on the three-week prescription that the chemist should only supply Shane with one week of the drug at a time, according to his father. But when Shane went to fill the second prescription, the chemist asked him if he wanted to get the three-week prescription filled at once, and Shane said yes. It was Friday 14 August. His family believe Shane took another high dosage of antidepressants the next day. In the early hours of 16 August, Shane Clancy carried out his attack.

"Shane was the type of person who was always careful about taking pills. If he had a Lemsip, he'd phone me to ask if he could take paracetamol as well a few hours later. I don't know if he was attempting suicide when he took three weeks' worth of antidepressants in one day. I might never know," says his father.

"I don't want to be seen as pointing the finger at the doctors or the chemist but surely if it said to only give him one week's supply at a time, the chemist should have followed that instruction."

Patrick believes no one should be put on antidepressants unless they're already undergoing counselling and that St John's Wort, the herbal treatment for depression, should still be available without prescription. "I think some people do need antidepressants. But the number of young people who are taking them is frightening and they seem to be very easy to get, as you know."

In the aftermath of the tragedy in Bray, the Sunday Tribune visited five GPs and reported feeling depressed. Four of the five prescribed antidepressant medication. The purpose of this investigation was to establish how easy it would be to obtain a prescription for antidepressants under false pretences and highlight that people looking for help have a wait of several weeks or months for counselling in the public service.

"I think every parent should ask their GP where they stand on antidepressants and in what circumstances they would prescribe them to their children. We all need to look at the relationship between doctors and pharmaceutical companies. Shane put a high dosage of chemicals into his body and I've no doubt he reacted to that. Some people take antidepressants and they don't agree with them. The consequences of that can be horrific."

A joint inquest into the death of Shane Clancy and Sebastian Creane in the coming months could provide some answers for the two grieving families. It is possible that the two GPs who prescribed antidepressants as well as the chemist may be called to give evidence as to his state of mind.

"It's easy to dramatise what happened. But we have to look at the bigger picture and ask why," says Patrick. "I hope that out of Shane and Sebastian's death some­thing constructive can happen. We all never think things like this can happen to us. I did too until I got that knock on my door."