Physical abuses by U.S. military police of Iraqi prison detainees stemmed from a mixture of soldiers' anger and frustration over poor working conditions, their racism and the absence of any meaningful supervision, according to the report of an Air Force psychiatrist who studied the episode for the Army.

The unclassified report, by Col. Henry Nelson, provides the military's principal, internal explanation for why the soldiers participated in the abusive actions. His independent study was based on a review of thousands of pages of interview transcripts and other documents the Pentagon has not released, and it is appended to a report of the Army investigation headed by Maj. Gen. Antonio M. Taguba.

At the Abu Ghraib prison in Baghdad, "the worst human qualities and behaviors came to the fore" in an atmosphere of "danger, promiscuity and negativity" within a closed environment, wrote Nelson, a member of the Army's investigating team. He noted training lapses, as others have, but also said that soldiers' unfamiliarity with Islamic culture, their pervasive sense of danger and the indefinite nature of their tenure were factors that wore them down.

"The sadistic and psychopathic behavior was appalling and shocking," Nelson wrote in the report, which was provided to The Washington Post by a government official. "Abuse with sexual themes occurred and was witnessed, condoned [and] photographed, but never reported."

Much of the language in Nelson's study supports the Army's contention that the abuses were a product of a distorted environment at Abu Ghraib last year, amounting to a wartime version of the malicious conduct by marooned children in the novel "Lord of the Flies." But the report is at odds with recent congressional testimony by top Army and military intelligence officials that the prison abuse involved only low-ranking soldiers and was not known by more senior officers.

On Aug. 23, 2003, Nelson wrote, an intelligence officer "kicked and beat a passive, cuffed detainee who was suspected of mortaring Abu Ghraib." This incident, Nelson wrote, "was witnessed by officers and NCOs [senior enlisted officers] alike."

Military officials have generally described the abuses as a function of "aberrant behavior" and weak leadership within the military police units stationed at the prison, rather than as a result of orders passed down the military chain of command. Nelson's study, according to a brief summary given by Taguba, suggested the abuses were "wanton acts of select soldiers in an unsupervised and dangerous setting."

Some senators have said they suspect, to the contrary, that the abuses stemmed from a Washington-directed policy to encourage particularly aggressive interrogations during this period, involving an unusually close collaboration between military police who were guarding the prisoners and intelligence analysts who wanted to extract information from the detainees.

The collaboration deepened at the urging of an Army general sent from Washington last August to improve the efficiency of the intelligence-gathering process. Before then, the prison was run by the 800th Military Police Brigade; after a policy change formalized on Nov. 19, military police at two key cellblocks containing prisoners that posed a security threat were placed under the direct control of the 205th Military Intelligence Brigade.

Taguba said the collaboration violated Army doctrine, but senior Pentagon officials have challenged this view. Nelson did not address whether it was appropriate but confirmed that military police and intelligence analysts jointly perpetrated some abuses. In addition to the incident in August, he cited an Oct. 28-29 incident in which two military police beat up a prisoner suspected of involvement in a rape, at the specific instruction of "MI soldiers."

Witnesses -- including some of the abused Iraqis -- also told the investigators that "pairs" of interpreters and interrogators were involved in other abuses. Moreover, the military intelligence unit at the prison "seemed to operate in a conspiracy of silence," Nelson wrote, allowing the abuse to escape wider notice.

In highlighting psychological and cultural factors underlying the abuses, Nelson noted that soldiers sent to Iraq were immersed in Islamic culture for the first time and said "there is an association of Muslims with terrorism" that contributed to misperceptions, fear and "a devaluation of a people." He reported that one military police platoon leader was openly hostile to Iraqis, and that a police dog handler was "disrespectful and racist" -- attributing to his dog a dislike of Iraqi "culture, smell, sound, skin tone [and] hair color."

Nelson also described the climate at Abu Ghraib as grim and the living conditions as "deplorable" and dangerous, a circumstance that he said provoked some of the U.S. soldiers' anger and hostility toward their prisoners.

The prison was "lacking most of the amenities at other camps," the Iraqi guards were corrupt, and "all present . . . were truly in personal danger," Nelson said. A weapon was smuggled into the camp, mortars rained on the facility every day, and prisoners sporadically rioted, leading to "numerous injuries for both soldiers and detainees alike."

The prison has "both depressive and anxiety-laden elements that would grind down even the most motivated soldier and lead to anger and possible lack of control," Nelson said. He drew a contrast between the current detention mission and procedures during Operation Desert Storm, the first U.S. invasion of Iraq, in 1991, in which most detainees were held only briefly before being repatriated.

The present war, he said, is "ongoing, with no end in sight." Every day, he said, "the soldiers deal with . . . extraordinary frustrations and hostile detainees who are in total limbo concerning their fate and release." The prison guards and intelligence officers also were under pressure from their U.S. military leaders, he wrote, to "either prevent escape or obtain intelligence rapidly." Some of the abuses were committed by "MP and MI soldiers" as retribution, Nelson said. The soldiers were "especially indifferent and vindictive towards detainees involved in any violence towards coalition forces or who exhibited deviant behavior."

A prisoner who smuggled in the weapon was shot in the legs, and then a military police soldier ripped off his bandages, beat him on his wounds, and hanged him by the arms until they became dislocated, Nelson reported. Police also stripped, tethered together and photographed some Iraqis suspected of raping a young boy in the prison, he wrote.

A vindictive attitude was not the only psychological problem, Nelson wrote. "Clearly some detainees were totally humiliated and degraded" by people who were practicing a "perversive dominance." He said the events were "a classic example" of the formula that "predisposition plus opportunity" can produce criminal behavior.

"Inadequate and immoral men and women desiring dominance may be attracted to fields such as corrections and interrogations, where they can be in absolute control over others" in the absence of appropriate supervision, Nelson wrote. He noted that two men suspected as "ringleaders" in the abuses, Spec. Charles A. Graner Jr. and Staff Sgt. Ivan L. "Chip" Frederick II, "both had experience in corrections."

"They collaborated with other MP soldiers and several unknown MI personnel, to include soldiers as well as their U.S. civilian contract interrogators and interpreters," Nelson wrote.

Frederick and Graner are now awaiting court-martial. Graner's attorney Guy Womack did not return a phone call for comment; he has previously said Graner was only following orders from military intelligence officials. One of Frederick's attorneys, Gary Myers, has said his client acted under the direct supervision of military intelligence officers.

It is important, Nelson wrote, "to remember dominance in and of itself is not improper. In fact, interrogators knowingly dominate their subjects and sometimes intimidate their subjects. But clearly, behavior at Abu Ghraib crossed the line."

Nelson also emphasized that "command factors" set the stage for the abuse and allowed it to persist. He cited, in particular, friction between the police and intelligence commanders, poor training and supervision of the soldiers, and what he characterized as a "lenient" attitude by senior officers in the military police at the prison toward infractions of the rules.

The abuses at the prison, he said, were "common knowledge among the enlisted soldiers," but even some officers knew of them or witnessed them. Those involved took the view that the chain of command would "essentially do nothing" and believed "I can get away with this," Nelson wrote.

"There were several commanders and NCOs [among those studied] who were ineffective leaders," Nelson said. He singled out in particular Brig. Gen. Janis L. Karpinski, who commanded the 800th Military Police Brigade and was responsible for the prison until she was shunted aside by intelligence officers on Nov. 19 at the request of Lt. Gen. Ricardo S. Sanchez, the top U.S. military officer in Iraq.

Nelson said Karpinski had difficulty delegating work, dismissed punishments of lesser officers that were recommended by her staff, and was ineffective in resolving problems with personnel, logistics, administration and supplies, of which she was aware. Karpinski "felt herself a victim and she propagated a negativity that permeated throughout" the area of her command responsibility, Nelson wrote.

One of Karpinski's attorneys, Fred Taylor, dismissed the claims in an official rebuttal, stating that Nelson was unqualified to make findings of fact. Taylor also said Army investigators had ignored statements by officers in her brigade "replete with praise and admiration of her clear guidance, firm, fair and common-sense enforcement of standards, [and] her caring for the soldiers."

In his summary, Nelson wrote that "the psychological factors of negativity, anger and hatred combined with a desire to dominate and humiliate within an unsupervised workplace" where no threat of punishment existed.

In his report, completed by early March, Nelson urged that a "competent authority . . . expedite the release of detainees." But it was not until April 23, after a group of Iraqi professors complained to the civilian U.S. administrator of Iraq, L. Paul Bremer, that Bremer announced a program to improve the detainees' processing and also to accelerate their release. Nelson also urged the military to have more psychological help available for soldiers in Iraq.

And finally, Nelson said, "we must be ever ready to prevent the recurrence of such inhumane behavior." The way to do that, he said, is to ensure that the guilty "face swift, appropriate justice."

A U.S. soldier stands guard at Abu Ghraib prison outside Baghdad. The stressful duty led some guards to commit abuses, an Air Force psychiatrist says.Col. Henry Nelson's study, appended to a report by Army Maj. Gen. Antonio M. Taguba, left, partially blamed Brig. Gen. Janis L. Karpinski's leadership.Spec. Charles A. Graner Jr., left, and Staff Sgt. Ivan L. "Chip" Frederick II had worked in corrections before and may have enjoyed the power, Nelson wrote.