The New York Times had quite the scoop last week, with an exclusive revelation that Donald Trump had lost so much money in 1995 that he probably has not paid taxes since. The Times published the story despite the pretty clear risk that doing so could land some of its newsroom (or its executive editor) in jail.

But how did the paper get the scoop? Turns out it was a good old-fashioned anonymous letter. Journalist Susanne Craig explains the story behind the story:

“I walked to my mailbox and spotted a manila envelope, postmarked New York, NY, with a return address of The Trump Organization. My heart skipped a beat.

“I have been on the hunt for Donald J. Trump’s tax returns. The Republican presidential nominee has broken with decades-long tradition and refused to make his returns public. I have written extensively about Mr. Trump’s finances, but, like almost every other reporter, I was eager to see his actual returns.

“The envelope looked legitimate. I opened it, anxiously, and was astonished.

“Inside were what appeared to be pages from Mr. Trump’s 1995 tax records, containing detailed figures that revealed his tax strategies. Almost immediately, I walked over to the desk of David Barstow — a three-time Pulitzer Prize winning investigative reporter and my teammate in the quest for Mr. Trump’s tax returns.”