So they found some stuff that had been buried in somebody´s backyard for 12 years.

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WASHINGTON (CNN) -- The CIA has in its hands the critical parts of a key piece of Iraqi nuclear technology -- parts needed to develop a bomb program -- that were dug up in a back yard in Baghdad, CNN has learned.

The parts were unearthed by Iraqi scientist Mahdi Obeidi who had hidden them in his back yard under a rose bush 12 years ago under orders from Qusay Hussein and Saddam Hussein´s then son-in-law, Hussein Kamel.

U.S. officials emphasized this was not evidence Iraq had a nuclear weapon -- but it was evidence the Iraqis concealed plans to reconstitute their nuclear program as soon as the world was no longer looking.

The parts and documents Obeidi gave the CIA were shown exclusively to CNN at CIA headquarters in Virginia.

Obeidi told CNN the parts of a gas centrifuge system for enriching uranium were part of a highly sophisticated system he was ordered to hide so as to be ready to rebuild the bomb program at some time in the future.

"I have very important things at my disposal that I have been ordered to have, to keep, and I´ve kept them, and I don´t want this to proliferate, because of its potential consequences if it falls in the hands of tyrants, in the hands of dictators or of terrorists," said Obeidi, who has been taken out of Iraq with the help of the U.S. government.

Centrifuges are drums or cylinders that spin at high speed and separate heavy and light molecules, allowing increasingly enriched uranium to be drawn off.

Former U.N. arms inspector David Kay, now in charge of the CIA search for unconventional weapons, started work two days ago in Baghdad. CNN spoke to him about the case over a secure teleconferencing line.

"It begins to tell us how huge our job is," Kay said. "Remember, his material was buried in a barrel behind his house in a rose garden. There´s no way that that would have been discovered by normal international inspections. I couldn´t have done it. My successors couldn´t have done it."

CNN had this story last week but made a decision to withhold it at the request of the U.S. government, which cited safety and national security concerns.

The U.S. government told CNN the security and safety issues have been dealt with and there is no risk now in telling the story fully.

The gas centrifuge equipment dates to Iraq´s pre-1991 efforts to build nuclear weapons.

Experts said the documents and pieces Obeidi gave the United States were the critical information and parts to restart a nuclear weapons program and would have saved Saddam´s regime several years and as much as hundreds of millions of dollars for research.

Obeidi said he felt unsafe in Iraq after the U.S.-led invasion and that he was getting pressure from different corners of the country.

He also said other Iraqi scientists were watching to see if he was safe after he cooperated with the U.S. government.

Now that he is safe, Obeidi said he believes other scientists would come forward with other components of Iraq´s weapons program.