America's privatised military machine is at the heart of the war on drugs in Colombia. Defence corporations hired by the US government enjoy extremely lucrative contracts, but who is responsible when something goes wrong?
Last year, I came across some dramatic footage of three US contractors held hostage by members of Revolutionary Armed Forces of Colombia (Farc), a 17,000 strong, left-wing guerrilla group who live deep in the jungle.
Why were these apparent "civilians" kidnapped and held captive for nearly two years?
I began my investigation by contacting one of the hostage's mothers, Jo Rosano. She told me about the crash of a tiny single-engine plane, which led to her son Marc's kidnapping.
Marc Gonsalves was employed by Northrop Grumman - the fifth biggest multinational defence corporation in the US - to help fight the war on drugs in Colombia.
The job involved dangerous aerial cocaine-eradication missions above the jungle, and on 13 February, 2004, the Cessna plane that Marc and four others were in experienced engine failure and crash-landed.
Two of the crew were killed and the other three - including Marc - were taken hostage.
Jo Rosano has a mother's rage and wanted answers. She believes more would have been done for her son Marc if he had been a soldier, not just an employee.
This is something the US ambassador to Bogota strongly denies. He told me: "The United States has no higher priority than the safe return of the American hostages in a manner consistent with US law and policy."
The official US position is that they refuse to negotiate with terrorist organisations like Farc, a group now viewed by the Bush administration on a par with al-Qaeda.
I approached Marc's employer, Northrop Grumman, for some answers.
They stonewalled me, just as they had done Jo.
I did, however, come across some letters written by two disgruntled employees and former pilots working for this company in Colombia.
Doug Cockes had 30 years' professional experience flying on drug missions.
He was one of the "whistleblowers" who had alerted Northrop Grumman's vice-president to the fact that the single-engine planes used to fly out on the dangerous coca surveillance missions over guerrilla-controlled territory were not adequate.
I flew to Colorado to interview him.
He told me: "If I could just talk to one of the people that could have made the change from single to twin engine, I would ask them how they sleep at night."
He explained that his written warnings of imminent disaster to Northrop Grumman and the US State Department - who had issued the contracts - were ignored.
Two months after his prophetic letters were sent, two planes had crashed in the Colombian jungle, resulting in deaths and hostage-taking.
So why outsource foreign conflicts to multi-billion dollar private military corporations, if there are concerns about the safety of hardware?
Political heavyweights, both in Colombia and the US - including Defence Secretary Donald Rumsfeld - suggest that it is more economical to use contractors, rather than regular troops, because the army is stretched beyond capacity.
An alternative opinion held by other US politicians is that "corporate soldiers" make it possible for the government to avoid responsibility.
The 40-year narcotic-funded conflict in Colombia between US and Colombian government troops, Farc guerrillas, and more recently, right-wing paramilitaries, is far from simple.
Perhaps this is even more reason to stop private companies acting on matters of foreign policy.
I met the widow of Tommy Schmidt, a Vietnam war hero and one of the Northrop Grumman pilots killed in the second crash.
She is filing a lawsuit against Northrop Grumman and the US Defence Department, accusing them of negligence, gross mismanagement and the death of her husband.
"Northrop Grumman offered me $350,000 (£180,000)," Sharon said, "but in taking that money I had to agree not to ask any more questions, and the whole point of all of this is that I want answers to our questions. I refused their offer."
Across the US and in Colombia I began to uncover a multi-layered world of military contracts, sub-contracts and brass plate subsidiaries. It seemed that profits, not patriotism, prevail in the business of war.
Interviews with US and Colombian politicians, contractors on the ground and big players in the military corporate world made me question whether American taxpayers were getting value for their $1.1bn annual funding for private war.
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