We have a desperate need to make sense of those terrible 82 seconds in Westminster last week when a man who called himself Khalid Masood laid a trail of death, misery and pain at the feet of the mother of parliaments.
There are a number of possible narratives, each as unsatisfactory and partial as the next. At first sight, the attack looked every bit the classic Islamic State copycat attack in the style of Berlin or Nice. The modus operandi of mowing down tourists and members of the public in a very public place certainly looked very “IS”.
But now, the police tell us there is no evidence of a connection with international terrorism.
What other stories can we tell to explain this? Was Khalid Masood — or Adrian Elms or Adrian Russell Ajao — a simple psychopath or did his triple-personality suggest a whole series of alternative narratives of suffering and hate?
Was he radicalised in prison? It appears not.
Did he have links to the usual suspects of British radical Islam? We don’t know.
Khalid/Adrian was, so we are told, a popular schoolboy sportsman, a violent criminal capable of slashing another man’s face in a pub argument, a cocaine fiend, an English teacher of some kind, an oppressive Islamist father and, on the eve of the attacks, a jovial hotel guest.
Neil Basu, the Metropolitan Police’s Deputy Assistant Commissioner expressed a common frustration when he said: “We must all accept that there is a possibility we will never understand why he did this. That understanding may have died with him.”
But Mr Basu did not stop there. “I know when, where and how Masood committed his atrocities,” he added. “But now I need to know why. Most importantly, so do the victims and families.”
There is a desire, a very human need to know more, even in the most desperate of situations.
Meanwhile, politicians turn to policy solutions because it is what they do. Amber Rudd announced a possible ban on end-to-end encryption on social media because Masood was thought to have used WhatsApp.
The police announced that security will be tightened around Parliament and Windsor Castle: future-proofing against further inexplicable atrocities. Something has to be seen to be done amidst all this not understanding.
What could ever explain someone driving at 70 mph along a busy pavement into real flesh-and-blood human beings?
What fuels someone who drives a knife into an unarmed policeman? What anger, what sense of victimhood or injustice could make a man do that? What psychosis? What evil?
Kenan Malik provided the wisest of the instant commentary last week when he identified the “continuing degeneration of Islamist terror and increasingly blurred lines between ideological violence and sociopathic rage”.
It is too easy to forget the case of Zakaria Bulhan, the teenage Norwegian-Somali schizophrenic who knifed several people in London’s Russell Square last year, or the mentally disturbed Syrian refugee who hacked a woman to death with a machete near Stuttgart. These were initially thought to be jihadi attacks but turned out to be nothing of the sort.
We may yet discover that Khalid Masood was under the command of the IS leadership from Mosul who used WhatsApp to give him his final instructions. But deteriorating mental health is a more likely explanation.
His story is probably closer to those of Michael Adebolajo and Michael Adebowale, the Islamic convert killers of British soldier Lee Rigby, whose jihadi credentials were limited to the occasional woeful cry of “Allahu Akbar”.
There is another narrative. It is that sometimes people are just pure evil. They are murderers and that is that. David Cameron said as much in response to the case of Raoul Moat, the Geordie bodybuilder who in 2010 shot his ex-girlfriend, killed her new partner and blinded policeman David Rathband before killing himself in an armed stand-off with the police.
“It is absolutely clear that Raoul Moat was a callous murderer, full stop, end of story,” Mr Cameron said.
But there is never an end to such stories. No full stop.
Perhaps the most brilliant piece of extended journalism in recent years is Andrew Hankinson’s You Could Do Something Amazing with Your Life [You are Raoul Moat]. Written entirely in the second person, it is a direct challenge to Mr Cameron’s analysis. The prologue ends: “You have nine days and your whole life to prove you are more than a callous murderer. Go.”
In Moat’s case there was a wealth of material to draw on to explain what he had done: from Moat’s own psychotherapy questionnaires and audio diaries he kept, to the trial transcripts of those who helped the murderer.
Moat was convinced he was the victim of a police vendetta as his life collapsed around him following a break-up from his girlfriend. Mr Hankinson is determined to allow Moat the space to explain how he had become so filled with rage that he was prepared to shoot a policeman in the face.
I am wary of quoting Primo Levi in this context. He is too often used as a secular prophet. But he stared so hard at the philosophical problem of irrational hatred that sometimes he seems like the only person who has done enough thinking about the horror of the inexplicable. He makes an important distinction between knowledge and understanding.
He suggested there are some categories of human-made atrocity that should be beyond understanding.
“Perhaps one cannot, what is more one must not, understand what happened, because to understand is almost to justify,” he said of the Holocaust in the afterword to If This is a Man.
“We cannot understand it, but we can and must understand from where it springs, and we must be on our guard. If understanding is impossible, knowing is imperative, because what happened could happen again.
“Conscience can be seduced and obscured again — even our consciences. For this reason, it is everyone’s duty to reflect on what happened.”
We have learnt so much since September 11, 2001. We now know extremist Islamists driven by a deep hatred of enlightenment values are prepared to hit soft civilian targets in major cities; we know antisemitism sits at the heart of the murderous ideology behind these attacks; we know young British Muslims are not immune to the attractions of jihad; we know converts are among some of the most active new recruits and that prison provides a breeding ground for extremism.
Will any of this help us understand those 82 seconds in Westminster? Probably not. It is only human to try to make sense of it, but in the end it makes no sense.