Michael Byers, Fellow in international law, Oxford University, Legal adviser to the Chilean victims of Augusto Pinochet

I was approached last month by a group of Chilean victims and organisations such as Amnesty International and asked to put together a case for prosecuting the former Chilean dictator Augusto Pinochet.

Pinochet had just been arrested at a London hospital and the English High Court was shortly to rule on whether to allow his extradition to Spain. Spanish judges want him to stand trial for some of the many crimes alleged in the extradition warrant, including torture, crimes against humanity and genocide - all committed during Pinochet's 17-year military rule in Chile.

I wrote an opinion arguing that under international law Pinochet, even as a former head of state, was not entitled to immunity. The High Court did not accept the argument and the case went to the House of Lords.

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On Wednesday, by a three to two majority, the Lords denied Pinochet immunity. It is a landmark ruling in international law that has put the rights of human beings above the rights of states. From now on, if a head of state allows torture or genocide then he or she will be held responsible for those crimes.

The Lords ruling is in accordance with UK international obligations, although there was some question as to whether English national law allowed them to enforce those obligations. Having had the rules of international law for 50 years, we now see that any national court has the right to enforce them.

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The Lords' message to the world is that human rights matter. I have nothing but praise for the three judges. Next Wednesday, Pinochet will be required to attend Bow Street magistrates' court to decide whether there is sufficient evidence for him to be extradited to Spain. That is a judicial decision but, given the allegations in the extradition warrant, I think there is a good chance the magistrate will rule for extradition.

Much of the expertise in international law is found in universities. Academics have been particularly well placed to advise on this case and this is a small victory for them. Pinochet is one of the century's villains and putting him behind bars is important.