The events in downtown Baghdad's al-Nisour Square on September 16, 2007, were a defining moment in the Iraq War.
Guards employed by United States security firm Blackwater Worldwide fired on Iraqi civilians. The incident fuelled insurgency and epitomised everything that had gone wrong in a disastrous military adventure that continues to reshape the Middle East.
This month, seven years after US prosecutors charged five Blackwater contractors, four men appeared in a US District Court in Washington.
Nicholas Slatten, a former US Army sergeant, is charged with murder. Paul Slough, Evan Liberty and Dustin Heard, variously veterans of the US Army and US Marine Corps, are accused of voluntary manslaughter, attempted manslaughter and gun charges. All have pleaded not guilty.
At the height of the conflicts in Iraq and Afghanistan, contractor personnel outnumbered troops in each theatre of war.
The indictments were unsealed in December 2008 when prosecutors alleged "that at least 34 unarmed Iraqi civilians, including women and children, were killed or injured without justification or provocation by these Blackwater security guards". The case against the fifth guard, Donald Ball, was dismissed in September last year. A sixth guard, Jeremy Ridgeway, pleaded guilty to voluntary manslaughter in December 2008.
Prosecutors now say the accused killed 14 Iraqis and wounded 18.
The defence contends that on September 16, the defendants were guarding a convoy of armoured vehicles carrying US diplomats -- Blackwater provided protection to staff from the US State Department -- when they came under fire in al-Nisour Square. The four men say they returned fire in self-defence.
As proof they cite multiple bullet holes in one of the vehicles, radio logs and spent shell casings from AK-47 assault rifles found in three places.
But prosecutors say the accused fired indiscriminately for about 15 minutes. A US military report said the incident "has every indication of an excessive shooting", there was no evidence Iraqis fired weapons and victims seemed to be fleeing.
Anti-Iraqi sentiment may have been a factor; in 2004 four Blackwater contractors were killed in Fallujah and their charred bodies hung from a bridge.
Prosecutors say the defendants tried to cover up their actions.
They also say it took four days for State Department investigators to survey al-Nisour Square and that they "seemed bent on clearing the contractors". The department gave the Blackwater guards "limited use immunity" after the shootings, promising nothing they said would be used against them in court, a legal get-out that hampered prosecutors.
State did not respond to Herald requests for comment.
Meanwhile, in a trial expected to last months, defence lawyers face an uphill battle in finding witnesses to corroborate claims the accused were ambushed. Instead, they have tried to undermine the prosecution's case by insisting witnesses colluded with Iraqi police to manipulate testimony.
Speaking last November to promote his memoir, Civilian Warriors, Erik Prince, the US Navy Seal who co-founded Blackwater in 1997 (the company was rebranded as Xe Services in 2009, then sold and renamed Academi in 2011), insisted some Iraqis were killed by AK-47 fire and that the rifle was "not a US weapon". But the Senate Armed Services Committee heard in 2010 that a Blackwater employee working for Paravant (a shell company created to deceive officials) withdrew more than 200 AK-47s from a US armoury in Afghanistan using an alias lifted from TV's South Park.
Speaking to talkshow host Charlie Rose in 2007, Prince said the priority at al-Nisour was to get "the persons we're protecting off the X" -- the ambush point -- as quickly as possible. He insisted guards were rigorously trained veterans, and that out of 16,000 Protective Services Detail missions, firearms were used "in less than 1 per cent". Nonetheless, a House of Representatives committee found that in 125 incidents Blackwater fired first 80 per cent of the time.
A far less flattering take on Blackwater is provided by Jeremy Scahill's bestseller, Blackwater: The Rise of the World's Most Powerful Mercenary Army. He says it morphed from a small police security training firm into a post-9/11 behemoth, tasked with guarding VIPs in Iraq and Afghanistan. Scahill says some al-Nisoud victims were shot in the back and the incident showed how Blackwater worked independently of US military command.
Freedom of Information requests reveal drunkenness, drug use, sexual misconduct and the reckless use of weapons by DynCorp, Xe and Triple Canopy guards the State Department used in Iraq, Afghanistan and elsewhere.
Despite other shootings, including two guards prosecuted for killing two Afghans and wounding a third in 2009, a probe into claims Blackwater tried to bribe Iraqi officials after al-Nisour, a lawsuit brought by victims, and tales of a cowboy culture, the firm's revenue ballooned from US$400,000 ($456,530) in 1998 to US$1 billion by 2006.
Blackwater operatives also loaded Hellfire missiles on to Predator drones in the CIA's missions against suspected al-Qaeda leaders, an operation then kept secret from Congress.
During the past decade the US military, which numbered 1.4 million active personnel and almost a million reservists in 2001, has had to outsource tasks to maintain its global military reach.
"At the height of the conflicts in Iraq and Afghanistan, contractor personnel outnumbered troops in each theatre of war," Phillip Carter, a senior fellow at the Centre for a New American Security wrote in the Washington Post last year.
Says Janine Davidson, a security expert with the Council on Foreign Relations, "Contractors have been a constant presence since the Vietnam War. They remain a critical component in military logistics, hauling fuel, ammunition and other materiel, about 90 per cent of the total used in Afghanistan."
DynCorp, with annual revenues of US$3.4 billion, provide security (the firm replaced Blackwater when State voided its contract in 2009). Contractors even provided high-level officers in Iraq and Afghanistan to free up soldiers for combat says Davidson.
Meanwhile, after helping create a private army for the United Arab Emirates, with his new firm, R2, Prince is looking to provide guards to tackle Somali pirates as he canvasses opportunities in Africa. The call has gone out for contractors to transport materiel and security outfits already have boots on the ground. Business is booming.