We cleared out the investigations team conference room and, with our colleagues Megan Twohey and Russ Buettner, started drawing up a battle plan.

We obsessed over the documents, the envelope, the postmark, the date on the postmark — everything. We even checked every other mailbox on the third floor — and there are hundreds of them — in case the tipster had mailed additional documents to any other reporter.

We then came up with a list of people who could confirm the veracity of the tax records. The list was short.

Next, we set out to develop a portrait of Mr. Trump’s finances from the period in question, to see if we could support what the documents showed — that he had taken a huge loss in 1995 that could have allowed him to avoid paying federal income taxes for nearly two decades.

We were skeptical as we examined the tax records, though much of the information looked accurate. They were signed by Mr. Trump’s wife at the time, Marla Maples, and by Mr. Trump, whose recognizable handwriting renders his signature in jagged, oversize letters. Other details matched up.

But, of course, we needed a lot more before we could publish an article.

We were initially thrown off by a quirk in the records noticed by Megan: On the line on which Mr. Trump had reported his huge loss — of $915,729,293 — the first two digits did not line up with the next seven. Could the document have been doctored?

We hired tax experts to guide us through the math. We researched the 1995 tax code. We reached out to anyone who might have viewed Mr. Trump’s records during that period.