Much of SOD's work is considered confidential and according to Shiffman and Cooke, documents from the program show that law enforcement officers have been instructed to obscure SOD's involvement in cases, through something called "parallel construction." That's where police have to "recreate" investigations along a different track from the original tip, in order to wipe SOD's fingerprints from the case.

For example, the SOD might receive a tip from a wiretap or NSA intercept directing them to track down a specific vehicle that might be involved in a drug crime. They would then pass that tip along to the FBI or a local police department. But because they wouldn't want the police to reveal where they got the tip from, the officers would have to find some other excuse to stop the vehicle and begin their own independent investigation. Police would then go forward as if the traffic stop was their first clue, not the SOD tip.

The situation is compared to laundering money in order to obscure its source. But that could also mean entire cases being built on faulty or illegally obtained evidence. Even if it isn't, the secrecy involved could compromise the judicial proceedings. When and if the suspect goes to trial they might never discover the original evidence that led to their arrest, possibly creating a constitutional violation of the right to a fair trial. If the defense does find out about the "parallel construction," the whole case could be thrown out due to improper gathering of evidence.

There's also the further complication that many of the tactics that are legal when used against a drug lord from another country (like warrant-less wiretapping), are illegal when used against American citizens. It's possible for an NSA tip to indirectly lead to an arrest of American — and for that original tip to be covered up by SOD.

Like all government surveillance projects, SOD seems to have started with just a handful of agents and ballooned beyond its original mandate. But one big question is: Does it even work? One former agent told Reuters the SOD tips were only accurate about 60 percent of the time. Also, because the agency was so worried that the program would be exposed if a case went to trial, defendants who refused to plea bargain and instead asked to see the evidence against them would sometimes see their charges dropped simply to avoid getting SOD involved. A lot of people might be fine with pushing the boundaries of legality to catch terrorists, but to push the boundaries to not catch American drug dealers is another story.

This article is from the archive of our partner The Wire.