EXCLUSIVE: The Case for Israel's Strike on Syria

Oct. 19, 2007— -- Israeli officials believed that a target their forces bombed inside Syria last month was a nuclear facility, because they had detailed photographs taken by a possible spy inside the complex, ABC News has learned.

The Bush administration has steadfastly refused to say anything about the Israeli raid on Syria, or to confirm what was hit. But ABC News has learned of the apparent mole and other dramatic and secret details about the events leading up to the airstrike, plus the evidence that supported it.

A senior U.S. official told ABC News the Israelis first discovered a suspected Syrian nuclear facility early in the summer, and the Mossad — Israel's intelligence agency — managed to either co-opt one of the facility's workers or to insert a spy posing as an employee.

As a result, the Israelis obtained many detailed pictures of the facility from the ground.

Watch the Full Report Tonight on "World News With Charles Gibson"

The official said the suspected nuclear facility was approximately 100 miles from the Iraqi border, deep in the desert along the Euphrates River. It was a place, the official said, "where no one would ever go unless you had a reason to go there."

But the hardest evidence of all was the photographs.

The official described the pictures as showing a big cylindrical structure, with very thick walls all well-reinforced. The photos show rebar hanging out of the cement used to reinforce the structure, which was still under construction.

There was also a secondary structure and a pump station, with trucks around it. But there was no fissionable material found because the facility was not yet operating.

The official said there was a larger structure just north of a small pump station; a nuclear reactor would need a constant source of water to keep it cool.

The official said the facility was a North Korean design in its construction, the technology present and the ability to put it all together.

It was North Korean "expertise," said the official, meaning the Syrians must have had "human" help from North Korea.

A light water reactor designed by North Koreans could be constructed to specifically produce plutonium for nuclear weapons.

When the Israelis came to the CIA with the pictures, the U.S. then got the site's coordinates and backed it up with very detailed satellite imagery of its own, and pinpointed "drop points" to determine what would be needed to target it.

The Israelis urged the U.S. government to destroy the complex, and the U.S. started looking at options about how to destroy the facility: Targeters were assembled, and officials contemplated a special forces raid using helicopters, which would mean inserting forces to collect data and then blow the site up.

That option would have been very daring, the official says, because of the distance from the border and the amount of explosives it would take to take down the facility.

The options were considered, but according to the official, word came back from the White House that the United States was not interested in carrying out the raid.

But as ABC News reported in July, the Israelis made the decision to take the facility out themselves, though the U.S. urged them not to. The Bush administration, with Secretary of State Condoleezza Rice and Defense Secretary Robert Gates leading the way, said the Israelis and the U.S. should "confront not attack."

The official said the facility had been there at least eight months before the strike, but because of the lack of fissionable material, the United States hesitated on the attack because it couldn't be absolutely proved that it was a nuclear site.

But the official told ABC News, "It was unmistakable what it was going to be. There is no doubt in my mind."