I didn't learn until later that their mission in helping me had an underlying purpose: to prove how inept the Dutch had been and how savage and inhumane the natives were.

Monte and his crew of cut-throats hire Peter, a local guide who can speak the Asmat dialects. Finally, they enter the waterways that had drawn Rockefeller further and further inland in his search for rare artefacts.

We had sent a party ashore and were awaiting their return when there was the unmistakable sound of rapid gunfire from the village. I was worried, but nobody else on board seemed to have the slightest concern.

When the shore party returned, Peter gave me some information which I thought needed to be followed up. I asked him if he could go back the next day. All Peter would say was: "Too late, too late." Then it dawned on me exactly why it was too late. The gunfire wasn't the boys shooting a few wild boars: they were killing the villagers. The Indonesians were using this trip to conduct a little tribal murdering.

I was appalled. The boat journey into hell continued for around two weeks. I'd lost many kilos in weight. It was a nightmare of mosquitoes, headhunters, foul drinking water and now cold-blooded murder. One day, as we anchored, I slipped on some oil and fell off the boat. Usually the river was dead still, but an unexpected swell threw me off balance and into the water where crocodiles and sharks lurked. I couldn't get back on board fast enough.

I'd expected we'd sail up to a beach, shake hands with a few elders, hand over some gold and beads, and bring home a skeleton in a casket draped in the US flag. Never in my wildest thoughts had I imagined it would be like this; not to be able to shower or brush my teeth or even sleep.

Finally, we were getting closer to the tribe. It began to rain endlessly.

Everything was damp and mist settled like low-lying cloud. The crew had grown quieter, even more threatening. Conversation seemed pointless, as if each kilometre up the river made us somehow more primitive, as if we were journeying into the dark of our own soul.

We had now gone as far as we could in the patrol boat. From here on it would be in rubber dinghies and on foot. We went as far as we could in the dinghies then had to carry them and the outboards through the swamp.

Most of the time you were wading through knee-high water, then every now and again you would suddenly fall into a hole and find yourself up to your neck in mud. There were plenty of crocs around. Snakes were everywhere - up trees, on land, in the water - wherever you stepped.

The place had an evil aura about it. It was dank, dark and dangerous. At night we stuck cottonwool in our ears to stop bugs crawling in.

After just a few hours of these conditions your clothes were soaked through with a mixture of your own perspiration and the foul waters you'd been wading through. The chafing, the discomfort, as you trudged through mud was terrible.

I had been keeping the anxiety at bay pretty well up to this point, but when I saw dark shapes in the distant trees my stomach knotted up. The shapes in the trees were rotting corpses. I didn't know if this was an Asmat burial ground or what, but it spooked me. Nothing was normal, nothing was what it seemed. I started praying, something I hadn't done in years.

The second day of our trek took the surrealism of the scene to new heights.

Suddenly, we emerged into a small clearing to find two tribes confronting one another, ready for battle. The warriors wore nothing but penis gourds. Some had their hair decorated with long bird plumes, most carried spears and shields.

The two tribes quickly turned their attention away from each other towards us. There were many more of them than us but we were heavily armed. I don't know who fired first. Dieter and I were in the middle of the squad when the fighting started. There was gunfire, then spears and arrows were coming our way. One of the commandos went down, struck by a spear as his fellow soldiers raked the natives with automatic fire. After a couple of minutes the locals just ran off into the jungle.