Despite assurances from top intelligence officials that the National Security Agency only conducts certain surveillance operations to pursue suspected terrorists, a report from Reuters alleges that a secretive Drug Enforcement Administration unit is using NSA data to launch criminal investigations of US citizens for drug crimes. In a troubling twist, Reuters reports that the DEA is covering up its relationship with the NSA by training federal agents to retroactively recreate the investigative trail in an effort to conceal its NSA leads.

Reuters reports that the effort by the DEA's Special Operations Division (SOD) has resulted in the agency essentially lying to defense lawyers, prosecutors, and even judges about how their investigations began. As The Washington Post notes, the issue is troublesome because of the blurred lines between foreign and domestic investigations, which permit different tactics; the NSA is a military intelligence agency that is supposed to conduct spying on non-US citizens, whereas agencies like the DEA and FBI are tasked with domestic criminal investigations that must respect the constitutional rights of US citizens.

The DEA's process for concealing the origin of its leads is called "parallel construction." As Reuters explains, parallel construction may be legal in establishing probable cause for an arrest — but using it to hide how an investigation began could violate the rules of pretrial discovery by keeping useful evidence from defendants. "It's just like laundering money," a former DEA agent told Reuters. "You work it backwards to make it clean."

Neither the DEA nor the Department of Justice returned The Verge's request for comment by the time of publication.

News of the DEA's collusion with the NSA comes as pressure mounts for intelligence agencies and top government officials to reveal more information about the extent of domestic surveillance programs. While President Obama's administration has broadly defended the NSA's activities, Congress is divided on key laws that have enabled the NSA to justify programs like a phone surveillance dragnet that collects records on every call placed within the United States.

Part of the problem is that the public — and even Congress — doesn't know the full extent of the NSA's capabilities, or the legal justifications behind them. And despite several congressional hearings on domestic spying programs, top intelligence officials have obfuscated the full truth, leading some lawmakers to call for the resignation of Director of National Intelligence James Clapper.

When asked in June whether the NSA collected "any type of data at all on millions or hundreds of millions of Americans," Clapper replied "not wittingly." A leaked court order revealing that the NSA regularly asks Verizon for all metadata associated with its customers phone calls showed Clapper's statement to be false.

Now, as Reuters has revealed, it appears the worst fears of some civil liberties advocates and government surveillance critics have been realized.

"When law enforcement agents and prosecutors conceal the role of intelligence surveillance in criminal investigations, they violate the constitutional rights of the accused and insulate controversial intelligence programs from judicial review," ACLU deputy legal director Jameel Jaffer said today, regarding the DEA's actions. "This is inappropriate, dangerous, and contrary to the rule of law."