Soldiers and paramilitary police from Zimbabwe have broken ranks to speak out about a 2008 operation in which civilians working in the Marange diamond fields were massacred.
Some of those involved in the attacks have told BBC Panorama that civilians were encircled, trapped and fired upon with automatic weapons.
Civilians who were present during the attacks said people were gunned down as they attempted to flee in panic.
The soldiers, many racked with guilt over their own actions, told the BBC the massacre was part of a full-scale military operation ordered from senior levels in Zimbabwe's military.
Its purpose was to clear the diamond fields of freelance diamond diggers to pave the way for the military to take charge of the area. Military sources said that about 1,500 soldiers took part in the operation.
In the end there was no way out
Officer who trapped miners
The BBC collected testimonies from 53 witnesses and victims of the attacks, as well as a number of perpetrators, including military officers.
The military operation was known as "Operation Hakudzokwe", which translates as Operation "You Shall Never Return".
The Zimbabwean government has not responded to the BBC's latest findings, but had previously denied its troops carried out killings in Marange in late 2008 following reports of the killings by human rights organisations.
Marange's riches became publicly known in 2006 and are of great interest to the diamond industry.
"In the last 20 years, we haven't found a significant great new deposit. It was the most significant find in many, many years," said Chaim Evan Zohar, international diamond analyst.
Some Marange diamonds are now starting to reappear on world markets due to mixed signals from the Kimberley Process (KP), the joint industry, government and non-governmental organisation group that is mandated to prevent so-called conflict or "blood" diamonds from being sold on international markets.
The KP eventually imposed a sales ban on Marange diamonds in 2009, when reports of large scale killings and abuses a year earlier surfaced. But now there is disagreement over whether or not the ban is still in place.
Massacre in the blood diamond fields
The massacre investigated by the BBC took place in late October 2008 when Zimbabwe was in the depths of economic crisis. Thousands of civilians had flocked to the diamond fields in the hope of finding gems.
Among the victims were women and children, some working in a makeshift market which had sprung up to sell food and clothes to the miners.
Unknown to them, several weeks before the killings began, the military had started laying a circular trap around the civilians.
They laid strings of mines and ultimately stationed armoured vehicles, mounted soldiers and an infantry battalion in a circular pattern around the 2.5km area.
"In the end there was no way out," said an officer who was directly involved in laying the trap.
Warning shots were initially fired, but soon after soldiers and paramilitary police then began firing AK47's directly into those fleeing, said former soldiers and paramilitary policemen, who have since fled to South Africa.
Multiple civilian and military witnesses said soldiers fired down on civilians from military helicopters.
"Twenty to 30 people would die every day. I am talking about the ones I saw with my own eyes," said one officer involved in the attacks.
"Even those that had been injured were being finished off," said another witness.
Several people told of seeing groups of bodies left in shallow graves in the diamond fields, or loosely covered with leaves.
Many civilians were severely mauled by trained dog units. Two told the BBC the dogs bit them on their testicles while soldiers or police looked on.
"Vumbai", a 27 year old mother of two, was dragged into a bush by a soldier.
"He then raped me. I could hear other people screaming and crying, female voices. It meant they were being raped like me."
The BBC has confirmed that a mass grave, containing between 69 and 105 bodies, exists at Damgamvura Cemetery in Mutare, the main town near the diamond fields.
A man who worked in the cemetery, who wished to remain anonymous, witnessed the burials.
"The body parts were packed in black plastic bags. You could actually see the bones piercing through the plastic. Blood was dripping everywhere. It was disgusting."
A morgue worker who helped pack the bodies for burial said the bodies decomposed at the morgue, which was overcrowded and was suffering electrical power cuts at the time.
He said he helped pack 105 bodies which went to Damgamvura. Other sources put the number buried there at 69. The BBC has obtained morgue documents showing 88 bodies came in from the diamond fields during three weeks in late 2008.
Several former paramilitary police and soldiers told the BBC that the operation was commanded in the normal way for a large scale military operation.
"Without orders from the top this would not have been possible," said a military officer who was directly involved in Operation Hakudzokwe.
President Robert Mugabe is Commander in Chief of Zimbabwe's military.
The BBC has collected evidence from two eyewitnesses who saw General Constantine Chiwenga, next in command, in the town closest to the diamond area, Mutare, during the period of the massacre.
Separately, the BBC has confirmed that the helicopters deployed in the killings came from Manyame air base, where Air Marshall Perence Shiri, Zimbabwe's air force chief, is based.
Luis Moreno Ocampo, Chief Prosecutor of the International Criminal Court (ICC) in The Hague, said attacks of this nature would be considered crimes against humanity.
"I cannot make any comment on your specific case but crimes against humanity can be committed when there is a widespread killing, attacks against the civilian population or systematic attacks against civilian population," he said of the BBC's findings.
Together with President Mugabe, Perence Shiri has been accused of masterminding the Gukurahundi killings in the 1980s in which many thousands of supporters of Mr Mugabe's key political opponent, Joshua Nkomo, were killed over a two-year period - their bodies dumped in mass graves.
The International Criminal Court needs a UN referral to investigate
They have never been prosecuted, partly because those attacks pre-date the ICC, which was constituted in 2002.
While the fresh accounts of the 2008 massacre could prompt an opportunity for a new investigation, the ICC cannot launch an investigation without a UN Security Council referral.
This is because Zimbabwe is not a party to the International Criminal Court.
Currently there is not the international will to push for such a prosecution.
The international community is instead focusing more closely on how to use diplomacy to help foster a stable democracy in Zimbabwe, both in the immediate future and after President Mugabe, now 87, dies.
Behind the scenes there are global tensions over the merits of international justice, with many governments quietly opposing strident efforts at prosecution because of the negative impact they can have on diplomacy.
But there are no guarantees that Perence Shiri, Constantine Chiwenga and other giants of Zimbabwe's political and security structures who allegedly have been party to large scale killings, will not still loom large on the political scene in a future Zimbabwe.
Panorama: Mugabe's Blood Diamonds, BBC One, Monday, 8 August at 2030BST then available in the UK on theBBC iPlayer.