Provincial Advisory Role During My Lai: As Deputy Province Senior Advisor, Guinn was part of the U.S. advisory apparatus in Quang Ngai Province during the period of the My Lai massacre. Provincial advisors had access to intelligence about military operations and their effects on civilian populations, placing Guinn in a position to know about the aftermath of the March 16 operation.

Charges Filed and Subsequently Dropped: Guinn was charged by the Army following the Peers Commission investigation, which identified him as bearing responsibility in connection with the My Lai massacre and its aftermath. The charges were dropped before trial, continuing the pattern of near-total impunity for My Lai-connected personnel.

Failure to Report Civilian Casualties: Provincial advisors were positioned to receive reports about civilian casualties from Vietnamese sources, which often differed significantly from the official U.S. military after-action reports. Guinn's failure to report or escalate discrepancies between military claims of enemy casualties and the reality of civilian deaths contributed to the cover-up.

Quang Ngai Province Civilian Impact: Quang Ngai Province was one of the most heavily contested areas of the Vietnam War and suffered enormous civilian casualties from American operations. The provincial advisory team was aware of the impact on civilians but consistently prioritized military objectives over civilian protection.

Peers Commission Identification: The Peers Commission identified Guinn as one of the individuals who should face charges in connection with the My Lai massacre. The commission examined the role of advisory personnel in the information chain and found that advisors had access to information that should have exposed the massacre.