The alleged abuse of Iraqi prisoners by U.S. forces at a prison outside Baghdad and its repercussions dominated much of the news surrounding the U.S. occupation of Iraq. Following is a look at some of the major developments last week:

* Army Maj. Gen. Antonio M. Taguba, who investigated the abuses at Abu Ghraib prison, said the scandal was caused by the willful actions of a small group of soldiers and by "a failure of leadership" and supervision by brigade and lower-level commanders. He testified Tuesday before a Senate committee that he found no evidence that the misconduct was based on orders from high-ranking officers or represented a policy to stretch the legal limits on extracting information. Several senators challenged Taguba's assertion that low-ranking officers devised the humiliating measures on their own.

* Nicholas Berg, 26, was shown being decapitated by five masked Islamic militants in a fuzzy video posted on the Internet Tuesday. They claimed the killing was in revenge for the abuses at Abu Ghraib prison. U.S. intelligence officials have concluded that Abu Musab Zarqawi, a Jordanian who is said to have links to al Qaeda and is accused of organizing attacks against U.S. occupation forces, killed Berg, a Pennsylvanian.

* Defense Secretary Donald H. Rumsfeld testified before Congress on Wednesday that all authorized interrogation techniques at Abu Ghraib complied with international law on the treatment of detainees. On Thursday, he made a surprise visit to Iraq and vowed to punish those responsible for the prison abuse there. A day after his visit, 300 detainees were released from the prison. President Bush has publicly supported Rumsfeld in an effort to head off the growing pressure for the secretary's resignation.

* Members of Congress were shown many unreleased images of abuse in a private session run by the Pentagon on Wednesday. The images, which included photos of Iraqi corpses and U.S. troops having sex with each other, and previously undisclosed videos of at least one inmate ramming his head into a wall, convinced some legislators that the number of Americans who engaged in prison abuse is larger than previously thought. Rumsfeld, who has said he thinks the images should be released, has been told by Pentagon lawyers that they should not because their release could violate international rules against publishing pictures of prisoners that could be construed as demeaning.

* Three soldiers charged with the prison abuse have been ordered to face courts-martial. They are Staff Sgt. Ivan L. "Chip" Frederick II, Sgt. Javal S. Davis and Spec. Jeremy Sivits. The Army also filed criminal charges, including adultery, against a fourth, Military Police Cpl. Charles A. Graner. Three other soldiers have been accused of participating in the abuse. Sivits has offered to plead guilty and has given investigators a detailed account of how guards humiliated and beat detainees.