WASHINGTON (Reuters) - A federal judge threw out all charges on Thursday against five Blackwater Worldwide security guards accused of killing 14 Iraqi civilians in 2007, saying the U.S. government had recklessly violated the defendants’ constitutional rights.

U.S. District Judge Ricardo Urbina said prosecutors had wrongly used statements the guards made to State Department investigators under a threat of job loss.

The five guards were charged a year ago with 14 counts of manslaughter, 20 counts of attempt to commit manslaughter and one weapons violation count over a Baghdad shooting that outraged Iraqis and strained ties between the two countries.

The shooting occurred as the private security firm’s guards escorted a heavily armed four-truck convoy of U.S. diplomats through the Iraqi capital on September 16, 2007. The guards, U.S. military veterans, were responding to a car bombing when gunfire erupted at a crowded intersection.

The defendants -- Paul Slough, Evan Liberty, Dustin Heard, Donald Ball and Nicholas Slatten -- were employed by Blackwater Worldwide, known since February as Xe Services.

The company, based in North Carolina, lost a State Department contract involving security for the U.S. Embassy in Baghdad after the shooting.

The government had argued that whatever knowledge prosecutors and investigators may have had of the defendants’ compelled statements, they had made no use of them.

But Urbina found the compelled statements pervaded nearly every aspect of the government’s investigation and prosecution, and the government’s use of those statements “appears to have played a critical role” in each indictment.

“Accordingly,” he wrote, “the court declines to excuse the government’s reckless violation of the defendants’ constitutional rights as harmless error.”

Urbina said prosecutors and investigators, in their zeal to bring charges, had repeatedly disregarded warnings of experienced, senior prosecutors that their course of action threatened the prosecution’s viability.

The Justice Department said it was disappointed in the judge’s action. “We’re in the process of reviewing the opinion and considering our options,” Dean Boyd, a department spokesman, said in response to a question about whether the government would appeal.

Mark Hulkower, a lawyer for the defense team, welcomed the decision and said the team was “thrilled that these courageous young men can begin the new year without this unfair cloud hanging over them.”

Representatives of Xe Services did not immediately respond to a request for comment.

Urbina prefaced his opinion with a quotation from a landmark 1966 U.S. Supreme Court case, Tehan v. U.S.:

“The basic purposes that lie behind the privilege against self-incrimination do not relate to protecting the innocent from conviction, but rather to preserving the integrity of a judicial system in which even the guilty are not to be convicted unless the prosecution shoulder the entire load.”

A sixth Blackwater guard pleaded guilty late last year to charges of voluntary manslaughter and attempt to commit manslaughter, and agreed to cooperate with prosecutors.