Civilians were detained by the KLA and kept in prisons where some were killed

"What can you feel when you see those things?" he said. "It's something that is stuck in my mind for the rest of my life. You cannot do those things to people, not even to animals."

As the man talked, his mother paced nervously in the nearby kitchen. She was panicked and tears were streaming down her face.

"They'll kill him, they'll kill him," she moaned, clutching one of her grandchildren.

But her son persisted. We spent hours in the family's sitting room as our source detailed allegations of possible war crimes by KLA officers in a military camp in the Albanian border town of Kukes.

It was a crucial interview for a delicate story I have been investigating for years.

Mystery of the missing

Soon after the war ended in Kosovo, I started looking into the thousands of civilians who disappeared during and after the conflict. Many Albanian victims were dumped in wells or transported to mass graves as far away as Belgrade.

LISTEN TO THE FULL REPORT

But others - mainly Serbs - simply vanished without a trace. There were no demands for ransom, no news of any kind.

I had met sources who spoke vaguely about secret camps in Albania where Kosovo Serbs, Albanians and Roma were interrogated, tortured and in most cases killed.

I met another source who agreed to share important details about KLA prison camps. This man cut a very different profile.

He had returned from a successful career abroad to join the KLA in its fight for Kosovo's independence from Serbia.

The man was still proud of the goals he fought for, but he had become haunted by the treatment of civilians he had seen at a KLA prison camp. More than that, he said he felt angry and betrayed by KLA commanders who tolerated and even ordered the abuses.

"It didn't seem strange at the time," he told me as he described seeing desperate civilians locked in a filthy agricultural shed.

Now, looking back, I know that some of the things that were done to innocent civilians were wrong Former KLA Fighter

He said the civilians were Serbs and Roma seized by KLA soldiers and were being hidden away from Nato troops. The source believes the captives were sent across the border to Albania and killed.

"Now, looking back, I know that some of the things that were done to innocent civilians were wrong. But the people who did these things act as if nothing happened, and continue to hurt their own people, Albanians."

This man was one of eight former KLA fighters who revealed some of their darkest secrets from the war.

A soldier's story

Yet another source spoke of driving trucks packed with shackled prisoners - mainly Serbian civilians from Kosovo - to secret locations in Albania where they were eventually killed.

He recalled hearing two of the captives begging to be shot rather than tortured and "cut into pieces".

"I was sick. I was just waiting for it to end," the source told me. "It was hard. I thought we were fighting a war [of liberation] but this was something completely different."

A long silence over the atrocities has held strong throughout Kosovo

It has taken these men 10 years to speak to an outsider about the dark side of the war. They were breaking a code of silence that has held strong in Kosovo.

Very few Kosovo Albanians have publicly revealed crimes committed by their own side. And for good reason. Witnesses who have agreed to provide testimony for prosecutions of KLA commanders have faced intimidation and death threats.

Some have been killed, according to United Nations officials in Kosovo.

There is another reason. All the men we spoke with insisted they were Kosovan patriots and would take up arms again to defend the country's independence.

But that is precisely the point: independence - of a sort - arrived for Kosovo last year. Their wartime goal has been attained.

As one of the former KLA fighters told me: "Now is the time to be honest to ourselves and build a real state."

Crossing Continents: Kosovo was first broadcast on BBC Radio 4 on Thursday, 9 April 2009 at 1100 BST and repeated on Monday, 13 April at 2030 BST.

You can also listen to Crossing Continents on the BBC iPlayer or subscribe to the podcast .