The U.S. Army says it has reopened an investigation into the suspected bludgeoning death of a key Iraqi government scientist in American custody, a chemist who allegedly experimented with poisons on prisoners in the days of Saddam Hussein (search).

Mohammad Munim al-Izmerly (search), 65, is the only known weapons scientist among at least 96 detainees who have died in U.S. custody in Iraq. Questions have surrounded the death ever since his body was dropped off at a Baghdad hospital in February 2004, two weeks after he died.

When it first came to light in press reports last May, the U.S. military, newly under fire for prisoner abuse in Iraq, refused to answer queries about the chemist's death. Now, months later, the Army says an investigation has begun.

"The case was initially closed, but after further investigative review a determination was made to reopen the investigation," Army spokesman Christopher Grey told The Associated Press.

The Pentagon (search) would say nothing about the timetable or thrust of the inquiry. But Rod Barton, an Australian member of the CIA-led teams that questioned al-Izmerly and other weapons scientists, says such prisoners may have been beaten during the futile U.S. hunt for banned arms in Iraq.

When al-Izmerly's body was delivered to Al-Kharkh Hospital, the Americans enclosed a death certificate saying he died of "brainstem compression," without saying what caused it, Britain's Guardian newspaper reported after viewing the document last year. A subsequent Iraqi autopsy determined he was killed by a blunt trauma injury, a blow to the head, Iraqi doctors told Baghdad reporters.

New details are emerging about the role al-Izmerly played in Iraq's weapons underworld.

In contrast to a "distinguished chemistry professor," the portrayal in one press report last May, U.S. weapons investigators now say al-Izmerly was an early leader of Iraq's effort to make chemical arms, and an assassination specialist who once devised a "poison pen."

The Egyptian-born scientist had been in U.S. detention since April 2003. His family was allowed to visit him in January 2004 at the Baghdad airport, where he was believed held at Camp Cropper, a U.S. military detention center for "high-value detainees."

A month later they were notified by the Red Cross he was dead. His son, Ashraf, 22, told reporters that when he went to the hospital morgue to claim the remains, zipped up in a U.S. body bag, he saw an injury to the head. The dated death certificate indicated the Americans had held the body for 17 days.

The family commissioned an autopsy, which found the cause of death to be a blow to the head, the reports from Baghdad said. "It was definitely a blunt trauma injury," the Los Angeles Times was told by Dr. Kais Hassan, who performed the autopsy at Iraq's Forensic Medical Institute.

Army spokesman Grey said the Army's Criminal Investigation Command lists al-Izmerly's death in an "undetermined cause" category because the body was released before Army investigators learned of the case, and no U.S. autopsy was performed.

Ashraf al-Izmerly, contacted this week by the AP, said he was aware of the reopened investigation, but couldn't immediately discuss the case further. Because of apparently new Iraqi Health Ministry rules, an AP reporter was not allowed to speak with Dr. Hassan.

The scientist's family, who gave no indication they were aware of the nature of his work, said last year they believed the U.S. military was covering up the circumstances of al-Izmerly's death.

There have been other cases in which the U.S. military attributed to natural causes detainee deaths later found to have been caused by brutal American treatment. One-quarter of the detainee deaths in Iraq and Afghanistan have been investigated as possible criminal homicides, according to U.S. government data reported by AP last week.

Charles A. Duelfer (search), the CIA special adviser who led the arms-hunting Iraq Survey Group, didn't respond to AP queries about what he knew of al-Izmerly's death. But Barton, one of his former subordinates, has spoken out.

The Australian microbiologist says he was told in February 2004, while working with Duelfer's group in Baghdad, that al-Izmerly died of a brain tumor. But "I had suspicions that this person had actually been beaten to death in the prison," Barton said in an Australian Broadcasting Corp. interview last month.

He said he saw two other detainees, also weapons hunters' interrogation subjects, with face injuries he thought were the result of beatings.

Contacted by the AP, Barton wouldn't elaborate on his suspicions, citing the sensitivity of testimony on the weapons hunt he is to give to the Australian Senate next week.

Al-Izmerly figures prominently in Duelfer's final report of Oct. 6, as a "mentor" to Iraqi chemists trying to make poison gas for military use in the 1970s, as leader of the effort to produce mustard gas, and in the 1980s as chief of an Iraq Intelligence Service chemical section.

In the intelligence role and earlier, ex-colleagues told interrogators, al-Izmerly was head of human experiments, testing substances for use on assassination targets by giving poisoned food or injections to some 100 political and other prisoners, the Iraq Survey Group reported.

This CIA account said al-Izmerly admitted administering poisons to 20 human subjects, but he said it was under orders from above. How many may have died is not reported.

One informant cited in the U.S. report said al-Izmerly in the 1980s ordered the fashioning of a poison-tipped pen for use in assassinations, and personally filled it with snake venom. It wasn't clear whether such pens were ever used.