The two senior DEA officials, who spoke on behalf of the agency but only on condition of anonymity, said the process is kept secret to protect sources and investigative methods. "Parallel construction is a law enforcement technique we use every day," one official said. "It's decades old, a bedrock concept."

A dozen current or former federal agents interviewed by Reuters confirmed they had used parallel construction during their careers. Most defended the practice; some said they understood why those outside law enforcement might be concerned.

"It's just like laundering money - you work it backwards to make it clean," said Finn Selander, a DEA agent from 1991 to 2008 and now a member of a group called Law Enforcement Against Prohibition, which advocates legalizing and regulating narcotics.

Some defense lawyers and former prosecutors said that using "parallel construction" may be legal to establish probable cause for an arrest. But they said employing the practice as a means of disguising how an investigation began may violate pretrial discovery rules by burying evidence that could prove useful to criminal defendants.

[...]

The SOD's role providing information to agents isn't itself a secret. It is briefly mentioned by the DEA in budget documents, albeit without any reference to how that information is used or represented when cases go to court.

The DEA has long publicly touted the SOD's role in multi-jurisdictional and international investigations, connecting agents in separate cities who may be unwittingly investigating the same target and making sure undercover agents don't accidentally try to arrest each other.

SOD'S BIG SUCCESSES

The unit also played a major role in a 2008 DEA sting in Thailand against Russian arms dealer Viktor Bout; he was sentenced in 2011 to 25 years in prison on charges of conspiring to sell weapons to the Colombian rebel group FARC. The SOD also recently coordinated Project Synergy, a crackdown against manufacturers, wholesalers and retailers of synthetic designer drugs that spanned 35 states and resulted in 227 arrests.

Since its inception, the SOD's mandate has expanded to include narco-terrorism, organized crime and gangs. A DEA spokesman declined to comment on the unit's annual budget. A recent LinkedIn posting on the personal page of a senior SOD official estimated it to be $125 million.

[...]

Wiretap tips forwarded by the SOD usually come from foreign governments, U.S. intelligence agencies or court-authorized domestic phone recordings. Because warrantless eavesdropping on Americans is illegal, tips from intelligence agencies are generally not forwarded to the SOD until a caller's citizenship can be verified, according to one senior law enforcement official and one former U.S. military intelligence analyst.

"They do a pretty good job of screening, but it can be a struggle to know for sure whether the person on a wiretap is American," the senior law enforcement official said.

Tips from domestic wiretaps typically occur when agents use information gleaned from a court-ordered wiretap in one case to start a second investigation.