(CNN) An active duty Navy SEAL deployed in Mosul, Iraq, with Eddie Gallagher testified Wednesday that when Gallagher fired his sniper rifle at a man, he did so because they believed him to be an ISIS combatant, not a citizen as other witnesses have testified.

Joshua Graffam, testifying under immunity at Gallagher's military trial, told the court he was acting as a spotter for Gallagher, using binoculars and range finders to help his partner monitor targets on the day of the incident.

Graffam said he saw two men he thought were ISIS, and told Gallagher, who agreed.

Gallagher fired and appeared to hit one of the men in the upper torso, Graffam said on the first day the defense presented its case.

Graffam testified he doesn't know what happened to the man, but said the man was dressed in all black and he thought the man was between 40 and 50 years old, not elderly as other witnesses have testified.

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