DiCaprio thriller to shine a light on the murky world of the modern mercenary

They like to operate in the shadows. You will find them in every war zone, all over the world. They are heavily armed, but answer to no general. They do not indulge in the sort of high-minded rhetoric presidents and prime ministers trot out to justify wars, but they do plenty of the killing all the same. Their motive is more easily explained: they are there to make money.

They like to operate in the shadows. You will find them in every war zone, all over the world. They are heavily armed, but answer to no general. They do not indulge in the sort of high-minded rhetoric presidents and prime ministers trot out to justify wars, but they do plenty of the killing all the same. Their motive is more easily explained: they are there to make money.

This is the world of the mercenary, and it is one that prefers the rest of us to keep our noses out. But now the Hollywood movie star Leonardo DiCaprio is reportedly planning to make an action thriller about the dubious world of the mercenaries.

It should come as no surprise. Mercenaries have been quietly plying their trade for centuries - pretty much since war began. But these days business is booming for them as rarely before, and two high-profile court cases have shone a far from welcome light into their secretive world.

First there was the case of "Jack" Idema, the supposedly freelance bounty hunter now serving a 10-year sentence in an Afghan prison for running his own private prison in Kabul and torturing Afghans he suspected of Taliban links by hanging them upside down from the ceiling.

Then there was Simon Mann, the Old Etonian ex-SAS officer now serving a sentence in a Zimbabwean prison. He was convicted on charges of illegally buying heavy weapons, but that wasn't what caught the outside world's attention - it was the allegations that Mann had been involved in a planned coup in oil-rich Equatorial Guinea, and more particularly the allegations that Mark Thatcher and Lord Archer were in on the plan.

Now DiCaprio is to produce and star in a new movie about the world of the mercenaries, according to Variety magazine. He is said to want to make the as yet untitled thriller into a cautionary tale about the dangers of "outsourcing" war to private contractors.

Outsourcing war is precisely what the Bush administration has done. US soldiers in Iraq stay at military bases guarded not by other soldiers, but by private security contractors. Mercenaries guard Baghdad airport, and they used to guard Saddam's old palace where the US proconsul, Paul Bremer, was based before sovereignty was handed over to the US-appointed Iraqi government.

There are believed to be as many as 1,500 mercenaries from Britain in Iraq, where they can make as much as £600 a day. They are not subject to military discipline like soldiers. When the Abu Ghraib prison abuse scandal broke, there were concerns that some of the interrogations had been put in the hands of private contractors.

The question which still hangs over Idema is this: was he really a freelancer acting for himself, like Simon Mann - or was he part of the Bush government's "outsourcing" of war as well? Throughout his trial, Idema insisted he was working for the US government, but that they had cut him loose because of the scandal over torture in Abu Ghraib and Guantanamo.