In many of my articles over the past 13 years, I've been explaining how this works in various covert theaters of operation.
Here's another one.
To set the stage, read these three quotes from a March 18 Washington Post story, "NSA surveillance program reaches 'into the past' to retrieve and replay phone calls":
"The National Security Agency has built a surveillance system capable of recording '100 percent' of a foreign country's telephone calls, enabling the agency to rewind and review conversations as long as a month after they take place."
"The voice interception program, called MYSTIC, began in 2009. Its RETRO tool, short for 'retrospective retrieval,' and related projects reached full capacity against the first target nation in 2011. Planning documents two years later anticipated similar operations elsewhere."
"At the request of US officials, the Washington Post is withholding details that could be used to identify the country where the system is being employed or other countries where its use was envisioned."
Comment:
Germans intercept condom-packaged cocaine headed to the Vatican