One widely cited source is the 2004 report by the U.S. Senate Intelligence Committee, which concluded that the CIA had used "enhanced interrogation techniques," which many consider to be torture, against detainees held in secret CIA facilities abroad, including those located in Iraq. The report found that the use of these techniques was not effective in obtaining valuable intelligence and had actually led to the production of false information.
Another prominent source of information is the 2006 report by the International Committee of the Red Cross (ICRC), which detailed incidents of torture, humiliation, and other ill-treatment of detainees in U.S. custody. The ICRC report noted that the allegations of abuse were not limited to a few isolated cases, but rather were widespread and systematic in nature.
In addition to these reports, there have been numerous allegations of torture and abuse made by individual detainees, human rights organizations, and other independent observers. These allegations include cases of beatings, electric shocks, waterboarding, and other forms of physical and psychological abuse.
It is important to note that the U.S. government has consistently denied the allegations of widespread torture and has claimed that the use of force was limited to justifiable and necessary measures to obtain information from suspected terrorists. However, the numerous credible reports and investigations that have documented instances of torture in Iraq suggest that these practices did indeed occur and that they were not isolated incidents.
Given the limited availability of reliable data and the challenges in conducting a comprehensive investigation in a post-conflict environment, it is difficult to provide a precise figure for the number of people who were tortured in Iraq. However, the existing evidence strongly suggests that torture was practiced by U.S. forces and their contractors and that it affected a significant number of individuals during the U.S. occupation of Iraq.