A former Blackwater security contractor was sentenced to life in prison Wednesday for taking part in a mass shooting at a Baghdad traffic circle in 2007 that killed 14 unarmed civilians.

A federal jury convicted 35-year-old Nicholas Slatten, of Sparta, Tenn., of first-degree murder in December. Prosecutors said that Slatten was the first of a group of four contractors to open fire in the shooting that killed 10 men, two women and two boys, ages 9 and 11.

Defense attorneys claimed that Slatten mistakenly believed that a potential suicide car bomber was moving toward his convoy. Friends and relatives of Slatten pleaded with U.S. District Judge Royce Lamberth for a lenient sentence, to no avail.

EX-BLACKWATER CONTRACTOR GETS MURDER CONVICTION TOSSED BY FEDERAL APPEALS COURT

Slatten's father, Darrell, spoke directly to his son, who was clad in a beige prison jumpsuit, saying: "Nick, please accept my apology for what your country has done to you. We will fight until hell freezes over to correct this travesty of justice."

Slatten's supporters believed he was a government scapegoat aimed at soothing tensions between the U.S. and Iraq over the heavy use of private military contractors in the Middle Eastern country. Slatten himself told the court that he was a victim of an "unjust prosecution" and that government lawyers placed a higher premium on securing a conviction than uncovering the truth of what happened in Baghdad 12 years ago.

"This is a miscarriage of justice and it will not stand," he said.

Lamberth disagreed, saying: "The jury got it exactly right. This was murder."

CLICK HERE FOR THE FOX NEWS APP

In 2014, a jury convicted Slatten and the three other contractors — Paul Alvin Slough, Evan Shawn Liberty and Dustin Laurent Heard— who were part of a four-vehicle convoy that was protecting State Department personnel at the time of the shootings. The original conviction was overturned on appeal, with an appeals court ruling Slatten should have been tried separately from the other three men.

Slatten was retried last summer, but a mistrial was declared after the jury couldn't reach a unanimous verdict. His second retrial ended in the December conviction.

The Associated Press contributed to this report.