Sergeant Lawrence Hutchins, who will stand trial for murder next month, made the comments after the abduction and killing of 52-year-old Hashim Ibrahim Awad in Hamdania outside Baghdad last April, a witness testified.
Navy medic Melson Bacos, who was jailed for one year last September for his role in Awad's killing, recounted Hutchins' comments while giving evidence at a sentencing hearing for another Marine, Trent Thomas.
Bacos said that after Awad had been shot in a roadside hole, squad members had to work quickly to remove "zip ties" used to bind his hands and feet.
The squad wanted to make it look like they had just come upon the victim, when in fact they had dragged him from his home, Bacos said.
"When all was cleaned up, Hutchins said, 'Congratulations. We just got away with murder, gents,'" Bacos told the hearing at the Marines' Camp Pendleton base outside of San Diego.
Prosecutors say Hutchins, who is to stand trial on March 19, was the ringleader of the plot to kill Awad.