Trump 'probably not the source' of leaked tax return, journalist who received document says David Cay Johnston said the document was delivered anonymously to his mailbox.

 -- The journalist who obtained and made public what are purportedly the first two pages of Donald Trump's 2005 federal tax return said this morning that the president was probably not behind the anonymous release.

"The venom and the anger and the falsehoods in the White House statement suggests that, no, he's probably not the source," David Cay Johnston told ABC News' "Good Morning America" today. "That tells me that this is somebody who either worked at the accounting firm or had connections to it or this copy was turned over to someone in a regulatory proceeding, in litigation, in a financial statement. And why not the whole return?"

Johnston said the two-page document was delivered anonymously to his mailbox and there was no return address on the envelope. He speculated Tuesday night that Trump — the first president in decades not to release his tax returns — or someone close to him was the source of the document. It's unclear where the document originated.

Johnston appeared on MSNBC Tuesday night to report on the document, which is stamped with the words "client copy" on the second page. The document shows Trump declared $103 million in losses in 2005, and his effective tax rate of 25 percent is well under the top income tax rate of 35 percent. But that rate is much higher than what fellow Republican Mitt Romney paid the year before he ran for the White House: just 14 percent.

It's also notable that Trump paid federal income tax at all in 2005. Although he has refused to discuss his income tax rate or release any documents, The New York Times reported last year that Trump's 1995 tax return showed he took a $916 million loss that "would have been large enough to wipe out more than $50 million a year in taxable income over 18 years."

The document does not show with whom Trump has done business, which, Johnston said, the president probably wants to keep private.

"I don't think he wants us to know all the people he's done business with, both those he's beholden to and those he receives income from," Johnston told "GMA" today.

Before Johnston's release of the information Tuesday night, the White House issued to ABC News a statement lauding Trump's income and taxes paid.

"Before being elected president, Mr. Trump was one of the most successful businessmen in the world, with a responsibility to his company, his family and his employees to pay no more tax than legally required," the White House said in a statement. "That being said, Mr. Trump paid $38 million dollars even after taking into account large scale depreciation for construction, on an income of more than $150 million dollars, as well as paying tens of millions of dollars in other taxes such as sales and excise taxes and employment taxes, and this illegally published return proves just that."

ABC News' Justin Fishel, Calvin Lawrence Jr. and Kelly McCarthy contributed to this report.