At an undisclosed location in Virginia, a publicity-shy DEA unit is feeding surveillance data from the National Security Agency (NSA), as well as wiretaps, informants, and a massive DEA phone record database, to law enforcement officials around the country to help them launch criminal investigations of American citizens. Reuters broke the story with an investigative report Monday.

Law enforcement has been directed to conceal how those investigations really began, deceiving not only defense attorneys, but also prosecutors and judges, raising serious questions about the propriety and even the constitutionality of the practice.

“The DEA increasingly qualifies as a rogue agency -- one that Congress needs to immediately investigate," "said Ethan Nadelmann, executive director of the Drug Policy Alliance. "This latest scandal may well be just the tip of the iceberg," he added, referring to the agency's checkered past.

"It's remarkable how little scrutiny the DEA faces from Congress or other federal overseers," Nadelmann continued. "With an annual budget of over $2 billion as well as significant discretionary powers, DEA certainly merits a top-to-bottom review of its operations, expenditures and discretionary actions."

The DEA unit in question is the Special Operations Division (SOD), which was created in 1994 to combat Latin American drug trafficking organizations. Its members also include the FBI, CIA, NSA, IRS, and Department of Homeland Security, among two dozen partner agencies. Since its inception, SOD has grown from several dozen employees to several hundred, Reuters reported.

Most of its work is classified and is intended to remain confidential. But Reuters managed to get its hands on key documents, including the one quoted from below.

"Remember that the utilization of SOD cannot be revealed or discussed in any investigative function," one document tells agents. It directs agents to not mention SOD participation in investigative reports or search warrant affidavits in courtroom testimony or discussions with prosecutors, instead instructing agents to use "normal investigative techniques to recreate the information provided by SOD."

In other word, to lie about the origin of information that becomes the basis for criminal prosecutions. DEA officials and former federal agents defended the practice, and one described the process to Reuters.

"You'd be told only, 'Be at a certain truck stop at a certain time and look for a certain vehicle.' And so we'd alert the state police to find an excuse to stop that vehicle, and then have a drug dog search it," the agent said.

Agents would then pretend that the investigation began with traffic stop, not with the tip from SOD, a practice known as "parallel construction." Surprisingly, senior DEA officials told Reuters the practice is nothing new and is used to protect sources and methods.

"Parallel construction is a law enforcement technique we use every day," one official said. "It's decades old, a bedrock concept."

But the practice could violate a defendant's right to a fair trial. Disguising the origins of information could violate pretrial discovery rules by obscuring evidence that could be helpful to defendants. And without knowing how an investigation began, defendants cannot know to ask to review potential sources of exculpatory evidence.

Legal experts pronounced themselves troubled by the revelations.

"I have never heard of anything like this at all," said Nancy Gertner, a Harvard Law School professor who served as a federal judge from 1994 to 2011, who along with others said the practice was more disturbing than the revelations that the NSA is collecting domestic phone records. "It is one thing to create special rules for national security," Gertner said. "Ordinary crime is entirely different. It sounds like they are phonying up investigations."

"That's outrageous," said Tampa attorney James Felman, a vice chairman of the criminal justice section of the American Bar Association. "It strikes me as indefensible."

A systematic effort to conceal the evidence that sparked criminal investigations "would not only be alarming but pretty blatantly unconstitutional," said New Jersey defense attorney Lawrence Lustberg.

"You can't game the system," said former federal prosecutor Henry E. Hockeimer Jr. "You can't create this subterfuge. These are drug crimes, not national security cases. If you don't draw the line here, where do you draw it?"

Even prosecutors have problems with the program. One federal prosecutor told Reuters that in one case, a DEA agent "misled" him, telling him an investigation of a US citizen began with an informant's tip. When the prosecutor pressed for more information, a DEA supervisor revealed that the information had actually come via the SOD from an NSA intercept.

"I was pissed," the prosecutor said. "Lying about where the information came from is a bad start if you're trying to comply with the law because it can lead to all kinds of problems with discovery and candor to the court."

The prosecutor never filed charges in the case because he lost confidence in the investigation, he said.

The SOD has claimed some "successes," including a 2008 DEA sting in Thailand aimed at Russian arms dealer Viktor Bout, who was convicted of conspiring to sell weapons to the Colombian FARC guerrilla army. It also coordinated Project Synergy, a crackdown on synthetic drugs that resulted in 227 arrests in 35 states.

"It was an amazing tool," said one recently retired federal agent. "Our big fear was that it wouldn't stay secret."