Further revelations have emerged about the US Drug Enforcement Administration's snooping on Americans' calls to international numbers – including the date it started and the operation that has since replaced it.

As The Register reported in January, court documents [PDF] revealed that the drug-busters were engaged in the bulk collection of US citizens' telephone metadata whenever a phone call was made to a country the agency was suspicious of.

An investigation by USA Today has now turned up more information, including details that the logs of "virtually all telephone calls from the USA to as many as 116 countries linked to drug trafficking," had been amassed for more than two decades in a program preceding even the terrorist attacks of 11 September 2001.

Although the operation has been discontinued, it is now the earliest known US government operation to collect its own citizens' telecommunications data en masse.

USA Today contacted "[m]ore than a dozen current and former law enforcement and intelligence officials" who explained that operation was initiated in 1992, under the administration of President George H W Bush. Its approval was ushered through by "top Justice Department officials in four presidential administrations and detailed in occasional briefings to members of Congress but otherwise had little independent oversight."

Following the terrorist attacks of September 2001, President George W Bush authorised the NSA to implement its own dragnet collection of Americans' telephone metadata. The United States Foreign Intelligence Surveillance Court (FISA Court) was made responsible for issuing the NSA's surveillance warrants, although the court has often been criticised as being little more than a rubber-stamp process.

The DEA, however, needed no court approval whatsoever. USA Today reports that narcotics agents searched the records "more often in a day than the spy agency [NSA] does in a year and automatically linked the numbers the agency gathered to large electronic collections of investigative reports, domestic call records accumulated by its agents and intelligence data from overseas."

"We knew we were stretching the definition [of what we were allowed to do]," said a former official described as involved in the process.

The operation was suspended in September 2013 following revelations of mass surveillance by the NSA and ultimately terminated. Explaining the methods which have replaced the program, USA Today reports that:

"Every day, the agency assembles a list of the telephone numbers its agents suspect may be tied to drug trafficking. Each day, it sends electronic subpoenas — sometimes listing more than a thousand numbers — to telephone companies seeking logs of international telephone calls linked to those numbers, two official familiar with the program said."

USA Today notes that the White House has made a similar proposal to end the NSA's Section 215 bulk telephony metadata program, authorised under the Patriot Act and set to expire on June 1. While the proposal if implemented would technically halt the NSA's bulk data collection, the number of US citizens targeted will likely remain high. ®