Washington (CNN) The second trial of a Blackwater contractor charged with first-degree murder for shooting unarmed civilians during the Iraq War has ended in a mistrial, according to US attorney spokesperson Bill Miller.
"A mistrial was declared in the case of Nicholas Slatten," Miller said in a statement. "The US Attorney's Office is reviewing the matter and has no further comment at this time."
Slatten of Sparta, Tennessee, was a sniper working for the private Blackwater Worldwide security company, contracted to the State Department to protect diplomats. He was accused of firing the first shots in a volley of machine gun and grenade fire that killed or injured 31 civilians in stopped traffic in Baghdad in September 2007.
Blackwater said the convoy Slatten was part of came under attack and had defended itself, but witnesses testified that the contractors had opened fire without provocation.
Slatten previously was found guilty of first-degree murder in the slaying of a driver in the Baghdad traffic circle and was sentenced to life in prison.
A federal appeals court overturned that conviction last year, and Slatten was then retried on the murder charge.
An FBI investigation found 14 of the deaths unjustified, according to rules of engagement for private security contractors in Iraq.
The Nusoor Square shooting exacerbated anger among many Iraqis at the security contractors in their country.
Blackwater lost its $1 billion contract with the State Department to protect American diplomatic personnel in 2009, after the Iraqi government refused to renew the company's operating license. The company was later renamed and sold.
Erik Prince, the firm's founder, grew close to Donald Trump's orbit during the 2016 presidential election campaign. He was a prominent Trump supporter during the campaign, spent time around senior transition officials and has continued informally advising the Trump White House on some major foreign-policy decisions.
Trump appointed Prince's older sister, Betsy DeVos, to lead the Department of Education.
CNN reported that Prince met with Trump and Gen. Michael Flynn during the campaign. He also gave $250,000 to pro-Trump efforts during the campaign, according to Federal Election Commission records.
Prince was recruited by then-White House chief strategist Steve Bannon and Trump's son-in-law, Jared Kushner, last summer to help devise a new Afghanistan strategy, according to The New York Times. He proposed replacing some US troops with private military contractors -- like the fighters employed by his former company, Blackwater, now known as Academi.
His ideas were met with heavy skepticism at the Pentagon and Trump did not embrace the plan at the time, but Prince has continued to pitch the idea in recent television appearances.