"The Post-Gazette has uncovered instances in which informants used to build federal cases were convicted murderers, liars or double agents working with both law enforcement and the targets. One informant with a violent past, used in a DEA case that ended in acquittal, wasn't put through the federal review process.
The results have included the indictment and incarceration of people whose lives were turned upside-down prior to their exonerations. Only nine people have been fully acquitted in federal court cases brought in Pittsburgh since 2009, but four of those not guilty verdicts involved shaky informants. Two of those exonerated defendants first spent years behind bars."
From the affidavits, the Post-Gazette constructed a picture of how often different federal agencies used informants in that jurisdiction. On average, approximately 40 percent of the affidavits relied on informants, but agencies diverged. For example, an article entitled "Gathering and Analyzing Data," the Post-Gazette explained:
"Confidential informants were much more prevalent in drug cases. Of the 94 cases led by the Drug Enforcement Administration or its task forces, 60 were built using confidential informants. Thus nearly two-thirds of the DEA's cases were based on secret sources. By contrast, the FBI used confidential informants in just under one-third of the 126 cases that stemmed from its affidavits. The Bureau of Alcohol, Tobacco, Firearms and Explosives used confidential informants in 13 out of 34 cases, or 38 percent, consistent with the average."
The last in the series here: Experts offer solutions to confidential informant problems.