Four teenagers are in police custody, arrested on suspicion of murdering the 16-year-old Ben Kinsella. There is talk of mistaken identity; whoever stabbed him got the wrong guy. Witnesses are afraid to speak out.

And we find ourselves, terribly, painfully, here again - the devastated family, the floral tributes, the smiling face of a child, the MySpace pictures, online memorials: “I remember when it was my birthday, when i blew out the candles on my cake you started to cry. so we lit them again and you blew them out. then i started to cry. you may be gone but you will not be forgotten,” a cousin, Jamie Marsh, wrote.

And another cousin, Hayley: “Ben i will never forget the time when you just a little baby and Debbie found a wasp in your nappy, still to this day we will never know if you ever swollowed it or not. You really was so cute in that blue buggy with the white spots!! I will miss you forever darling and I am sure your up there with your Grandad.”

I am so grateful that I cannot imagine what it must be like to be the mother of that little boy in the buggy, who cried when his cousin's birthday candles were blown out, the Arsenal fan, “bright kid” and talented art student planning to study graphic design at college.

And I have nothing but admiration for the lack of vindictiveness in the message that his mother and the rest of Ben's immediate family delivered yesterday, through his sister: “Hopefully he will be the one that finally puts an end to this. My family are determined to fight in his memory to make the streets safer for our children. Please, boys and girls, put down your knives and weapons and think about the pain and suffering they will cause.”

Nobody knows whether knife crime has exploded in the past few years. Official figures suggest not, but official figures are meaningless. While the Youth Justice Board reports a sharp increase in the number of teenagers arming themselves in the past five years, the British Crime Survey (BCS) suggests that knife crime has remained stable over the past decade.

Is it just tabloid hysteria? The BCS has only just begun to include data for children under 16, and younger victims are known to underreport. In many areas of the country, if you are stabbed in a street brawl, the last people you go to are the police - too many tricky questions to answer.

So let us ask Ben Kinsella. His family released to The Sun yesterday a creative writing essay that he wrote at school a few weeks back. “I've been stabbed,” he wrote. “Three times in the chest, twice in the back. Once in the gut for good measure. The pavement feels so very cold on my so very punctured back... As I stare up at my killer-to-be he feels not the slightest measure of remorse... he holds a phone to me and clicks a button. Flash, my misery a mere picture to broadcast the monstrosity society has become.” Ben dies and goes to heaven where he finds his grandad, and God - and a giant rave.

I'm not sure what I used to write about in creative writing classes when I was a teenager, but I am sure that it wasn't being “happy slapped” as I was stabbed to death on a cold pavement. Whatever the official figures tell us, these children's school stories tell us the truth - that teenagers are terrified of knives in the streets. When I was a child in Islington, North London, you were mugged - but you weren't stabbed.

The Government cannot decide how to respond to the hysteria over knife crime. It wants to turn its back on the penalising agenda of the Blair years, the ASBO society and the culture of fear. It wants to understand more than punish. But it also sees headlines, campaigns throughout the tabloids, holds emergency “summits” and talks up a new drive to prosecute over-16s for carrying knives.

It's such an easy thing to say. But the prospect of prison will not work on its own. It is too remote. Life inside is inconceivable to a teenager. It is as hard to get an 18-year-old to imagine standing in the Old Bailey with his life slipping between his hands as it is to persuade him of the danger of dying of lung cancer three decades' hence. Especially in the heat of the moment, when a teenager reaches for a knife to avenge some perceived wrong, the consequences are unimaginable to him.

I have seen a group of teenagers in the dock, after a situation as confused as Ben Kinsella's murder seems to have been. In the case that I saw, there was a gang of youths, whose car window had been smashed, who went to collect some friends to pursue the boys who had broken the window. At some point somebody picked up a knife and in the brief, ensuing fight two people got stabbed. One of them - not the target - died.

There was nothing cool about those young men I watched at the Old Bailey. All of them were given life sentences, with a minimum of 15 years. Every child in Britain, at the age of 12 or 13, should be forced to sit through a trial like that. Give them a mental image of the faces of those three defendants as they glanced ashamed at their parents in the gallery, pitifully dressed in their best clothes, pathetically young. They weren't all holding the knife; it was enough that they were there when somebody was stabbed. Not enough teenagers know that that is the law.

I ended up, indirectly, in touch with one of the defendants for a while. Let us call him David. David hadn't held the knife - even the judge had said so. His letters from jail - a young offender institution, then a tough adult prison - were searing. He was barely more than a boy. He loved football. His ashamed family had abandoned him. He couldn't believe this had happened, just in the flash of that moment. And he was dreadfully sorry. And nothing could be done for him.

I do not know whether the teenagers arrested for Ben Kinsella's murder are guilty. Nor, if they are, do I wish to suggest that I am sympathetic to them. They are not dead, and Ben is.

But I cannot help wondering whether, if whoever killed Ben had been linked, through their schools, with prisoners such as David; if they had seen the pathetic sight of David and his friends at the Old Bailey, witnessed the devastated mothers, heard the details of the dead body - and if they and not I had read David's letters, might Ben Kinsella not have had a better chance of being alive today?

I suppose No 10 will hold a “knife summit” again.

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