Somebody PLEASE name this movie!?

Hi there. I totally can not remember the name of this movie and its been bothering me. I believe I saw it in the theatre...definitly within the last 10 years..and NOT within the last couple years. I only remember fragments of the movie. Something about an investigation of a shooting among US soldiers? Turns out to be involved with drugs or some mive conspiracy? The main character is some government guy I think igned I think to figure it out? There's only a couple surviving witnesses..one is reluctant to talk until the main character shows he has history in the army and another starts violently throwing up nasty stuff before dying? The main general guy ends up disappearing? And then in the end...the main character tracks people to this i THINK latin american country (or at least they were celebrating mardis grae or dia de lose muertos) and he sees that the people who were supposed to have died in the incident were actually still alive and in on the "conspiracy?" I know..not