The government's recent announcement on young people in the justice system has led to debate about not just how young offenders can be prevented from reoffending but how young people can be prevented from offending in the first place.

Since I became a shadow Justice Minister a few months ago two incidents have particularly stuck in my mind. The first, an attack captured on CCTV in London. A youth is seen casually cycling down the road. He passes a shop and sees someone inside he recognises, or thinks he recognises. He takes out a gun, and casually shoots through the shop window. His target was most likely a member of a rival gang: but instead the boy hits an innocent bystander, and kills them.

The second, another piece of footage, from a prison for young offenders. Two inmates create a diversion while another group launches an attack on a boy sitting alone at a table, and beat him with ferocious violence. There was no clear motive. But like the first attack, what was striking was the way it was carried out with a total disregard for the consequences - either for the victim or themselves.

Serious youth crime is shocking because it clearly represents the squandering of life and potential not just for the victim but for the perpetrator. How can someone so young, with so much life to lead, carry out acts that are so cruel, and so reckless? It is a painfully clear indication that something in the environment in which that young life has been nurtured has gone terribly wrong.

That does not remove the personal responsibility of young people who commit crimes. The fear that they cause is real. The public have a right to be protected, and to expect that those who do wrong will face consequences. But there is no contradiction between this and the need to understand why youth crime happens and how the justice system can most effectively fight it - and a concern, if possible, to not waste two lives as well as one. That is good moral sense, but also good practical sense, because consigning offenders to the scrap-heap costs more, and leads to more crime.

Youth crime is a serious issue, accounting for a disproportionate 15% of offences. We should be careful not to reflexively declare some progressive social break-down: proven offences last year were actually down 47% from 2002. But there are clearly significant pockets about which we should have serious concern. That much was shockingly clear from the 2011 riots, let alone the smaller-scale incidents I have come across.

The roots of these problems are not uniform or simple, but there are some common threads: almost two thirds of the youths involved in the riots were from the poorest 20% of the country, and two thirds were classified as having special educational needs: among youth offenders in general most are from poor backgrounds. Half have been in care, and three fifths have communication difficulties. Better employment, better education, better skills and training, and better care are all needed to drive offending down.

So we need to think hard about rigorous, effective alternatives to prison for young offenders. We need to increase the involvement and coordination of different agencies in handling them, and make sure that, for those who do go into custody, the help needed to transition out to a life free of crime is better structured.

That includes better provision of education and training in secure environments and more effective help to establish work, accommodation and social services support on release. There are still too young people approaching the end of custody with nowhere to go - in every sense. That is one reason reoffending is a major problem: and why if you can change one young person's path, you can reduce crime.

In fact, it would be worth looking at extending some aspects of youth justice - like the ability to sentence offenders to secure training - to young adults up to the age of 21. We would need to consider many factors before making decisions in this area, not least any additional upfront costs that might arise but while their adult criminal responsibility is clear, offenders of this age face very similar circumstances to their 17-year-old peers, and are often little more mature than them. That's not just a matter of opinion: there is an increasing body of research that indicates the brain does not mature until the mid-twenties.

But of course, there are aspects of youth crime that are difficult for any government to address. What shocked me most from those two pieces of CCTV footage was the attitude they showed, the banal ease with which lethal violence was applied - a casualization of violence.

It is hard not to believe there is a cultural element here. I don't believe our kids are being turned into zombies by video nasties - we have some exceptional young people in our country; but nor do I think society is immune to what we consume and how we are brought up. The spread of easily available, and utterly degrading pornography, now accessible to every teenager with a smart phone; the growing incidence of single-parent families; child poverty, youth unemployment, availability of drugs, the cult of celebrity, the weakening of community ties.

Problems like these are never easy for governments to respond to even where the link is clear. But we must try. Young criminals need a firm hand: but we owe it to ourselves to use it intelligently. Because that is what will mean fewer wasted lives: both theirs and others.

This article was first published by Huffington Post on 3 February 2014.