WASHINGTON — One by one, four former Blackwater security contractors wearing blue jumpsuits and leg irons stood before a federal judge on Monday and spoke publicly for the first time since a deadly 2007 shooting in Iraq.

The men had been among several private American security guards who fired into Baghdad’s crowded Nisour Square on Sept. 16, 2007, and last October they were convicted of killing 14 unarmed Iraqis in what prosecutors called a wartime atrocity. Yet on Monday, as they awaited sentences that they knew would send them to prison for most if not all of their lives, they defiantly asserted their innocence.

“I know for a fact that I will be exonerated, in this life and the next,” said Paul A. Slough.

“I am very sorry for the loss of life,” Dustin L. Heard said. “But I cannot say in all honesty to the court that I believe I did anything wrong.”

“As God is my witness,” Evan S. Liberty said, he fired only at insurgents who were shooting at him.

“The verdict is wrong,” said Nicholas A. Slatten, a former Army sniper who was convicted of murder for starting the melee with a precision shot through the head of a young man stopped at an intersection. “You know I am innocent, sir.”