April 10, 2007  -- It was a simple letter, just more than 100 words on two pieces of paper.

But this singular document became one of the key pieces of evidence, the smoking gun, touted by the Bush administration to justify the invasion of Iraq. It's also the same piece of "evidence" that led to a perjury conviction for Vice President Dick Cheney's former top aide, I. Lewis Libby.

The July 2000 letter, which was obtained from Italian intelligence services, appeared to be an official correspondence from the Niger government to the president of Iraq, confirming a deal to sell 500 tons of pure uranium to Iraq annually.

But if the CIA had done a simple Internet search on some of the terms used in the letter, the agency would have quickly learned that it was a forgery.

Instead, the letter was later cited by President Bush in his 2003 State of the Union address as proof that Saddam Hussein was determined to build nuclear weapons, justifying a preemptive invasion of the country.

That revelation is one of the central themes of "The Italian Letter," a new book by Washington Post editor Peter Eisner and journalist Knut Royce.

"That document has mistakes in it that are sufficient to show that it's impossible that this operation could be real," Eisner told ABCNEWS.com. "Anybody, you or I, could have taken this and fact-checked this thing and we would have learned that this was nonsense. We would have learned that the organization in the letterhead hadn't been in existence for many years, that the person who signed it last served in that post in 1989 and that the court in Niger had been renamed in 1990."

If the CIA had done a Google search on the documents, it could have altered the course of history, according to Eisner and Royce.

Although the CIA was highly suspicious of the claims in the letter and didn't include it in a public white paper on Iraq's WMD arsenal, the letter was included in a report from the agency's Rome station.

That report was picked up by the Defense Intelligence Agency, which highlighted the erroneous claims about the agreement to sell 500 tons of uranium to Baghdad, and quickly caught the attention of Cheney.

But even if the letter had been sufficiently fact-checked, confirmation that the letter was a forgery might not have been enough to stop the administration's determination to unseat Saddam, according to the author.

"The Bush administration was looking for a way to go to war," Eisner said. "And they were looking at every possible means to go to war."

Some intelligence analysts are more skeptical about the ease with which the document could have been exposed and its potential impact on the path to war.

Anthony Cordesman, an ABC News consultant and the Arleigh A. Burke chair in strategy at the Center for Strategic and International Studies, believes that the story told in "The Italian Letter" is accurate and that "some people knew early on that this was not authentic and that this should have been communicated to the highest levels."

But he emphasizes that uncovering that the letter was a forgery might not have been as simple as a Google search.

"Most people can't detect a forgery," Cordesman said. "You are talking about a Third World country whose letterheads are uncertain at best. It's a country that many people don't know very much about."

And it's very unlikely that the letter's exposure could have stopped the drive to invade Iraq, he said. "It would have been just one of many, many indicators that people were discounting -- it was used because it was there. If it had not been in the presentation, it frankly wouldn't have mattered very much."

The documents had been peddled by rogue Italian intelligence agents to fellow spies and journalists, including Elisabetta Burba, a reporter for the Italian magazine Panorama, according to Eisner and Royce. After getting the documents from one-time security officer Rocco Martino, Burba found major flaws after 15 minutes of browsing the Internet.

When Bush cited the claims in his State of the Union speech on Jan. 28, 2003, Burba couldn't believe his words. "That was a story she'd had and hadn't written because she'd determined the information it was based on was bogus," according to the book.

Cheney's role as a cheerleader for the war almost ended up toppling him, the authors say. "Before the 2004 election, Karl Rove, the president's powerful political adviser, privately sounded out social and fiscal conservative activists who were unhappy with America's foreign adventurism, about the possibility of dumping Cheney as Bush's running mate."

The vice president soon found out about Rove's secret conversations and he was not happy. In the end, of course, Cheney stayed on the ticket. The White House has denied this account in the past. "This is ridiculous," spokesman David Almacy told ABCNews.com.

So, who wrote the letter and why did the media seem to accept its claims?

"Who wrote it? That's still unclear," Eisner said. "What is clear is that there was a rogue operation within SISMI [Italian military intelligence agency] that produced this material. There is a group of people inside SISMI running a secret safe house doing all kinds of operations and they've only been willing to speak to parliamentary inquests in Italy."

Although much of the mainstream media reported the explosive claims as fact, some TV outlets and newspapers expressed doubts.

"Many were sold a deal the same way that the administration did that to the Congress and to the American people," Eisner said. "The media loses some of its critical analysis in a run-up to war and instead there was a drumbeat -- the words 'mushroom cloud' were used repeatedly, battering the airwaves."