The sniper is on a roof-top opposite a playground. He has a child in his cross-hairs.

"You do what you have to do to stop him," says Jeremy Scahill. "I mean if you have to kill him that's unfortunate, but in a situation like that, law enforcement has a right to use deadly force. The problem for President Obama's drone programme is that America is not in a situation like that."

Scahill is the national security correspondent for The Nation, and the author of two books probing behind the scenes of America's post-9/11 wars, Blackwater: The Rise of the World's Most Powerful Mercenary Army, and Dirty Wars: The World is a Battlefield.

Scahill is a hard-left American liberal from a hard-left family. He dropped out of college in the early '90s and hitch-hiked to Washington DC to volunteer at a homeless shelter. He heard Amy Goodman's Democracy Now show and set out to get a job on it.


"So I learned journalism as a trade from someone who really believes in holding those in power accountable."

This is the core principle underlying Scahill's desire to scrutinise the Democratic Party's "pugilistic" foreign policy record, an attitude which won him a considerable amount of hate mail when he applied it to Barack Obama during the 2008 presidential campaign.

Scahill travelled to Afghanistan with documentary film-maker Rick Rowley in 2010, with the notion of working towards a full survey of Obama's war policies in action.

"The thing that caught our attention once we were there was the volume of night raids we were hearing about. No one seemed to know who was carrying them out ..."

One raid in particular put them on the path towards Dirty Wars and the accompanying film of the same name, which was short-listed for an Oscar. It emerged that American special forces soldiers had targeted the wrong house, killed a group of innocent Afghans and then dug the bullets out of the corpses in an attempt to cover up their mistake.

"We were able to obtain some video of the raid. That let us discover who was behind that raid and the others.

"From there ... we ended up following threads that took us to Yemen and Somalia and elsewhere."

They uncovered a pattern of wide-scale covert pre-emptive strikes, targeting potential enemies of America before they could develop terrorist plots.

This policy is in Scahill's view not merely immoral and unlawful, but also ludicrously counter-productive.

The example of the sniper targeting children in a playground is one Obama has repeatedly used to justify using drones for pre-emptive attacks.

"It could not be further from the reality we're discussing. We should go back to a law enforcement approach, and make the consequences for people who do engage in plots that get to an imminent stage very, very dire.

"I don't believe assassination is legal under international law. I don't believe it's lawful under American law. And I don't think it's a smart policy."

• Jeremy Scahill will speak at the Auckland Writers Festival on May 17.