The top U.S. weapons inspector for Iraq says the search for weapons of mass destruction has "gone as far as feasible" and has found nothing.

The assessment by CIA special advisor Charles Duelfer, head of the Iraq Survey Group, was contained in an addendum, posted on the Internet late Monday, to last year's final report on Iraq's weapons program.

Mr. Duelfer concludes there is no reason to keep many detainees who are held because of their knowledge of Iraq's weapons program , saying that after more than 18 months, the weapons investigation and debriefing of weapons-related detainees has been exhausted.

The United States maintains that the Iraqi authorities will make the final decision whether to release those detainees. Mr. Duelfer also warns that there is a risk some Iraqi scientists might share their skills with terrorists or insurgents, who are making concerted efforts to gain chemical weapons capabilities.