After the attacks of Sept. 11, 2001, came widespread shock and horror -- and some tough questions. Could the United States have prevented this catastrophe? What corrective action might we take to protect ourselves from other terrorist attacks?

After political struggles and initial resistance by many political leaders, Congress and the president created the Sept. 11 commission in 2002. This bipartisan group of 10 prominent Americans was charged with conducting an independent and complete investigation of the terrorist attacks of Sept. 11 and with providing recommendations for preventing such disasters. In July 2004 the commission released its report, and in December Congress passed legislation to implement many of its recommendations.

In the spring of 2004, the scandal involving the abuse of prisoners at Abu Ghraib became public. Additional allegations of abuse surfaced in connection with prisoners detained by the United States at Guantanamo Bay, Cuba, and elsewhere. Many Americans asked themselves the same painful questions about these allegations: How could such terrible actions have taken place? Who was responsible? What reforms might we implement to prevent such problems? Once again, a year later, these questions remain unanswered.

We believe that the American public deserves answers. We are members of the bipartisan Liberty and Security Initiative of the Constitution Project, which is based at Georgetown University's Public Policy Institute. We have joined with other members of the initiative -- Republicans and Democrats, liberals and conservatives -- to call for the establishment of an independent bipartisan commission to investigate the issue of abuse of terrorist suspects. We urge Congress and the president to immediately create such a commission and to use the Sept.11 commission as a model.

No investigation completed to date has included recommendations on how mistreatment at detention facilities might be avoided. Even the Pentagon's much-heralded report by Vice Adm. Albert T. Church, completed in March, concluded only that there were "missed opportunities in the policy development process" and that these opportunities "should be considered in the development of future interrogation policies."

Establishing an independent, bipartisan commission would also be beneficial for U.S. relationships abroad. The abuse of terrorist suspects in U.S. custody has undermined the United States' position in the world. This is a time when we should be making extra efforts to reach out to Muslims and to ask them to work with us in the war against terrorism. Instead, our failure to undertake a thorough and credible investigation has created severe resentment of the United States.

An independent, bipartisan investigation can generate widespread acceptance and support for its findings. Only with such a commission are we likely to enact the reforms needed to restore our credibility among the nations of the world.

We must move beyond the partisan battles of our highly charged political climate. To provide a credible investigation and a plan for corrective action, and to show the world that the United States takes seriously its obligations to uphold the rule of law, we urge Congress and the president to establish a commission to investigate abuse of terrorist suspects.

Floyd Abrams is a lawyer who specializes in First Amendment cases. Bob Barr, a former Republican representative from Georgia, deals with civil liberties issues for the American Conservative Union. Thomas R. Pickering, a former diplomat, has served as undersecretary of state and ambassador to the United Nations.