We never rely on one source. The first rule is for a minimum of two sources, and more if it's even more sensitive. A source is not just somebody who shows up one day, and then you publish the stuff. We usually cultivate the confidential sources we use for weeks and months, sometimes years. We get to know these people, to make sure that they are trustworthy and that what they actually tell us is true and believable. We have all kinds of safeguards to make sure that we don't fall into that kind of trap.
On June 19th, 2017. See this statement in context.