Given that Drug Enforcement Administration officials already have said 14-year-old Ashley Villarreal caused her own death, we shouldn't hold our breath for that agency's investigation into the tragedy. Can't police agencies learn to at least pretend they are conducting a thorough investigation before declaring their agents free of blame? The problem is, when juries get to examine all the facts, they often disagree: Take the case of David Aguilar of Three Points, Ariz., a small town outside Tucson. Aguilar wasn't 14, but 44. He had moved with his family from Tucson to get his children away from drugs and gangs....