Somewhere in the bureaucratic bowels of the Department of Homeland Security is a videotape shot above the Tivoli Gardens neighborhood of Kingston, Jamaica on May 24, 2010. It could reveal whether the Jamaican security forces, acting on behalf of U.S. prosecutors, killed 73 members of a notorious crime syndicate or innocent civilians caught in house-to-house fighting. That is, if anyone in a position of power actually wants that question answered.

Over 500 Jamaican soldiers rushed into the teeming Tivoli Gardens neighborhood that day for what became known as Operation Garden Parish, a mission...