Iraqi museums pillaged after the war were looted by organized thieves who knew exactly what they wanted and may have already taken priceless items out of the country, U.S. Attorney General John Ashcroft (search) said Tuesday.

Ashcroft spoke at an Interpol conference aimed at creating a database listing pieces of art and historical objects stolen in the aftermath of the war.

A main theme at the two-day Interpol (search) conference, which concluded Tuesday, was how much officials still don't know about the pillaging -- who carried it out, how organized the looting was and how many pieces are missing.

Ashcroft, however, said investigators have indications the looting was a professional job.

"From the evidence that has emerged, there is a strong case to be made that the looting and theft of the artifacts were perpetrated by organized criminal groups -- criminals who knew precisely what they were looking for," Ashcroft said.

His account matches comments by others -- including officials at Baghdad's National Museum (search) -- that at least some looters had access to museum keys and could distinguish copies from real pieces of art.

For example, looters who entered a reinforced storage area left three rooms full of artifacts untouched but almost emptied a cabinet at the back of the building containing hundreds of small -- but valuable -- ancient cylinders used as signature seals.

"It is clear that the person who did this had intimate knowledge of the museum and its storage practices," said Lt. Col. Matthew Bogdanos, who is leading a U.S. inquiry into the damage done by looters at the museum.

Ashcroft did not say whether he suspected international organized crime, such as the Mafia, but others at the Lyon conference said they had no such evidence.

"We are waiting for more information," said Jean-Pierre Jouanny, an Interpol specialist in theft of cultural objects.

Lack of reliable information has turned out to be a major obstacle to retrieval, experts say. Cultural officials say they have not been able to get access to records in Iraq that will help shed light on what pieces are missing.

Speaking in Baghdad, Bogdanos said that 38 items were missing from the main gallery, but museum officials were still trying to establish inventories for several external sites where artifacts were transferred before the allied invasion.

Every day, items are being returned to the museum, ranging from an inscribed cornerstone from King Nebuchadnezzar's 7th century B.C. Babylon palace to curios sold at the Baghdad airport gift shop.

Iraq's museums held millennia-old artworks from the Assyrian, Sumerian and Babylonian cultures. Ancient Mesopotamia -- modern-day Iraq -- was the cradle of urban civilization. Some experts fear thousands of artworks, including priceless antiquities, may be missing.

Interpol Secretary-General Ronald Noble said a top task was to collect and distribute descriptions of missing objects. He said such information was still sorely lacking.

"Right now, we are just operating on rumors and anecdotal evidence," he said.

Noble added that after the 1991 Gulf War, Interpol was able to log only one looted item into its database. That item was recovered two years ago, he said.

Another obstacle is the lack of a coherent police force inside Iraq.

Officials gathered in Lyon also discussed how far some of the looted goods have been moved from Iraq. While there is speculation that some Iraqi artwork has reached Europe, Jouanny and others said they doubt such movement is widespread.

Ashcroft, who pledged full U.S. participation and leadership in the retrieval of stolen art, said Washington would go after the thieves wherever they were.

"Although the criminals who committed the theft may have transported the objects beyond Iraq's borders, they should know that they have not escaped the reach of justice," he said, praising Interpol's efforts so far.

While the catalog at Baghdad's National Museum has been kept for the most part intact, the status of inventories at museums in other parts of Iraq is unknown.

A British Museum official who recently returned from Iraq estimated on Monday that 30 to 40 antiquities were missing from the National Museum in Baghdad. The fate of more than 100,000 pieces in storage, however, is unknown, he said.