Why do journalists sometimes use anonymous sources? How dependent is journalism on “leaks”?
The most credible journalism is transparent about its sources, identifying them whenever possible. However, especially in investigative reporting, sources can be reluctant to be identified for fear of losing their jobs or even coming to harm. Journalists make agreements to treat them as confidential sources whom they promise never to identify without being released from their agreements.
Famously, much of the Watergate reporting by Bob Woodward and Carl Bernstein of The Washington Post depended on such confidentiality agreements with sources who reached all the way up in the government to senior officials in the Nixon White House. None of those sources were identified while they were still alive. The Watergate stories usually referred to them only as "informed sources." With the exception of former FBI official Mark Felt, referred to until near his death only as "Deep Throat," Post editors knew the identities of all the Watergate sources, as editors should in judging the credibility of sources and stories.
Today many news organizations also require that anonymous sources be described, without violating confidentiality agreements, in ways that help audiences judge their reliability. Hence news stories often refer to "a senior government official" or "a source with knowledge of the investigation."
Because that still presupposes considerable trust of journalists and news organizations, anonymous sources should not be overused, as they too often are, just to avoid the trouble of persuading a source to go on the record. Government officials are especially eager to not be identified, even in routine stories, as the sources of "leaks."
Journalism in our democracy depends on officials being forthcoming with information about the people's business, including leaks from anonymous sources—whether authorized by government itself to reveal sensitive information without taking political responsibility, or by individual government officials who strongly believe the information should be made public. This is especially true of information classified as secret, the dissemination of which is legally risky for government employees. The federal government has been much more aggressive in trying to stop unauthorized leaks of classified information since the September 11, 2001, terrorist attacks.
During the Obama administration alone, six government employees, plus two contractors including the fugitive NSA leaker Edward Snowden, were subjects of felony criminal prosecutions for leaking classified information to the press under a 1917 Espionage Act, compared to three such prosecutions in all previous US administrations. In one of those investigations, the government secretly seized two months of call records for twenty telephones lines and switchboards in Associated Press bureaus in New York, Washington, DC, and Hartford, Connecticut, used by more than one hundred AP journalists on bureau, home, and mobile phones.
Journalists, of course, have a responsibility to do additional reporting to determine the veracity and context of information from leaks. More often than people realize, what may appear to be a purposeful leak is actually the product of a journalist aggressively seeking and gathering information from numerous sources and piecing it together like a puzzle. That was how, for example, The Washington Post's Dana Priest discovered the US Central Intelligence Agency's secret prisons for the interrogation of terrorist suspects in countries in Eastern Europe and Asia.