The spectre of murder-suicide that continues to haunt rural Ireland

Like Jonathan O'Driscoll's parents, eight-year-old Anthony's father refused to condemn his wife, who'd twice been admitted to psychiatric hospital for treatment, describing her as "a good person who made a mistake". She'd taken an overdose that night and was worried that there'd be nobody to look after her son when she was dead. She later received a seven-year suspended sentence at the Central Criminal Court.

Diane Ward's actions fit a common pattern of murder-suicide, the only difference being that the attempt to take her own life was unsuccessful. The murder of the O'Driscoll children doesn't follow any such obvious pattern, though it did bear some similarity to the murder of nine-year-old Brandon Skeffington by his brother Shane in Co Sligo a month earlier.

In that case too, the killer and his victim were said to be "great friends". Shane had been released from psychiatric hospital just days before the tragedy. Most murder-suicides are not like this.

Statistics show that the majority of perpetrators are men killing spouses and their children. Women may kill their children, but rarely their spouses. Usually, the killer and victim are in an intimate relationship and something has soured it. A quarter of cases of murder-suicide involve multiple victims, and over 75pc happen in the home, most commonly a bedroom (Thomas and Patrick were killed in their bedrooms).

In Ireland, there were more than 40 victims of such crimes between 2001 and 2013, and all but one of them occurred in rural areas.

In his book, The Perversion of Virtue: Understanding Murder-Suicide, Thomas Joiner, a professor of psychology at Florida State University, examined every single case he could find of these tragedies and came to the conclusion that, in order to understand them, one must begin by looking at the suicide. Whilst it may be the final act in the tragedy, it's the one from which the previous actions flow.

Two per cent of all suicides involve other victims. In those cases, Joiner asserts, a desire to die "necessitates, through an appeal to virtue, the death of at least one other person".

The phrase "appeal to virtue" seems odd, but is simply a reflection of the skewed thinking of the perpetrator at the time. He divides these "virtues" into four categories: justice, mercy, duty and glory.

Justice would include cases where a man kills his wife, and then himself, because she has been having an affair or is about to leave him to start a new life. In his mind, justice demands that she be punished first before he too dies.

Mercy might include parents who, having decided that they themselves should die, also kill their children, fearing that their lives will be worse if they don't. Duty most often involves an elderly person taking the life of a seriously sick spouse and then their own.

The worst of all is glory, as exhibited by the two teenage boys who carried out the massacre at Columbine High School in 1999, who, having no desire for life, wished to go out with a bang, not a whimper, and make the news headlines.

Jonathan O'Driscoll's act doesn't fit neatly into any of these categories, however, unless it was that he killed his brothers in an uncontrolled rage and then, filled with remorse, felt that he had to restore justice by punishing himself for the crime.

There is, however, the troubling question of that internet search. He'd also googled the phrases "Irish law, stabbing with a knife" and "science of suicide by hanging", as well as purchasing a knife two weeks before, suggesting that the murders were pre-planned.

The severity of the attack is also surely significant. The two boys were stabbed more than 40 times each, the inquest heard. Brandon Skeffington, by contrast, died of a single wound. There was a much greater level of rage in the O'Driscoll murders.

Who exactly was Jonathan, in his disturbed state of mind, punishing? What "virtue" was he seeking to enforce by killing his brothers? That they were his parent's biological children, and he, as an adoptee, had recently become consumed with knowing the details of his own birth, hints at one possible motive. Jonathan's mother, Helen, believes that it may be explained by a car accident in which her son was involved two years before he killed his brothers; and a study published in 2014 did find that 21pc of those who committed murder had suffered a "definite or suspected head wound in the past".

One example was the World Wrestling Entertainment star Chris Benoit, who killed his wife and child in Georgia before committing suicide. The finger of blame was initially pointed at his use of steroids, but repeated concussions that he suffered as a wrestler soon became the focus of inquiry, and post-mortem tests found that his brain "was so severely damaged, it resembled that of an 85-year-old Alzheimer's patient".

After Jonathan's head injury, Helen O'Driscoll said her son's behaviour changed. He grew quiet and depressed, and suffered paranoia, believing that he was being poisoned.

He also became convinced that she was holding back information about his birth family, and once slammed her against the wall whilst demanding answers. She was forced to seek a barring order against him, though she relented because he was so remorseful, and allowed him to come back home, with tragic consequences.

It's impossible to imagine the pain which she must now be enduring; interviews with her, including one with Keelin Shanley on radio midweek, were almost too painful to hear. But she's not alone.

A few days after Adam Lanza opened fire in Sandy Hook school in Newtown, Connecticut in December, 2012, killing 20 children and seven of their teachers, a mother wrote a blog detailing her own story under the chilling heading I am Adam Lanza'a Mother.

"I live with a son who is mentally ill," she wrote. "I love my son. But he terrifies me."

Her son had pulled a knife on her on occasions, threatening to kill her and then himself, once simply because she asked him to return overdue library books. He had two siblings, aged seven and nine. The family had a safety drill, whereby they had to run to the car and lock themselves in if their brother lost control.

"It's impossible to predict what will set him off," she said.

She used that experience to advocate for better treatment for those with psychiatric problems. The O'Driscolls have also urged those with problems to seek help before it's too late and for more resources to be provided to families going through this frightening experience alone.

Interestingly, both mothers use similar language to describe their sons. "When he's in that space, he's not him," said the American blogger.

As she sees it, mental illness is no different to cancer: both are diseases, and sufferers shouldn't be blamed.

"It was the sickness that killed them," was Helen O'Driscoll's way of putting it.

The couple even insist that they don't regret adopting Jonathan, which seems an extraordinarily benevolent statement to make; but the National Organisation for the Parents of Murdered Children in the US catalogues the difficulties which parents can face in the aftermath of tragedy - guilt at not having protected their children; agony at the thought of a child suffering. And in most cases, those who come through the horror are the ones who refuse to be consumed by bitterness or hatred.

The greatest torment of all is trying to make sense of it. Andrew Solomon, who wrote a book about Columbine, said he began with the idea that, the deeper he delved into what happened, the more he'd be able to explain it. Instead, meaning becoming more unknowable. The parents of those poor children understand that only too well.