They weren't. see:
No direct link ties Marine to deaths
Lt. Col. Jeffrey R. Chessani of Rangely lost his post after his unit was implicated in civilian slayings, but officials say the two actions may not be connected.
The Colorado Marine officer relieved of command after his unit was implicated in the deaths of as many as 24 Iraqi civilians in November is not necessarily suspected of participating directly in the killings, people familiar with the situation said.
Lt. Col. Jeffrey R. Chessani, 42, a highly decorated officer who grew up in the northwestern Colorado town of Rangely and served in the Gulf War and Panama invasion, was relieved of command of the 3rd Battalion of the 1st Marine Regiment, along with two of his commanders, on April 7 for what the military called "lack of confidence in their leadership abilities stemming from their performance during a recent deployment to Iraq."
From what I've read a marine sargent is the person of interest, not the commanders. I know few Colonels that go on patrol.