GATINEAU, Que. - Capt. Robert Semrau's court martial has been told one of those accusing him of a battlefield execution in Afghanistan was a "fairly erratic guy."

Maj. Steven Nolan has testified an Afghan soldier known as Rolling John came and told him: "Capt. Rob no good. . . . Capt. Rob boom boom Taliban."

Semrau, 36, faces second-degree murder charges for allegedly firing two rounds into the chest of a badly wounded and disarmed insurgent after an October 2008 ambush in Afghanistan.

Under cross-examination, Nolan agreed he encouraged military investigators to interview Rolling John but cautioned them that they may or may not trust him because he's a "fairly erratic guy."

Nolan testified there is a lot of "prejudice" among coalition forces against Afghan National Army soldiers and that he was trying to "culturally sensitize" Canada's National Investigation Service before they interviewed the Afghan witness.

Semrau's lawyer, Maj. Steve Turner, attempted to get Nolan to concede there is a problem of drug use in the Afghan army but the witness would only say Afghanistan has a cultural issue of drug use and the ANA is trying to change that culture.

Nolan is the second prosecution witness at the ground-breaking court martial.