Ambassador Walker served as MEI's President and CEO for over five years, from 2001 until August 2006.
But Ambassador Walker blamed the rebels for the civilian casualties.
But Ambassador Walker rejected the charge.
Ambassador Walker was among those who said it was not clear whether the United States officer had received his information from Colonel Aviles before or after the killings.
Ambassador Walker then said she was not credible.
Beforehand, the U.S. Embassy gave him a tape of Ambassador Walker's interview.
Ambassador Walker was recalled to protest the hanging.
Ambassador Walker declined requests to comment on Arena politics.
A Pledge of Protection Immediately after the killings, President Cristiani and Ambassador Walker pleaded for information about them and publicly pledged to protect anyone who came forward.
"That's untrue," Ambassador Walker said of Father Tipton's statement.