Joost Hiltermann, who was the principal researcher for Human Rights Watch between 1992–1994, conducted a two-year study of the massacre, including a field investigation in northern Iraq. His analysis of thousands of captured Iraqi secret police documents and declassified U.S. government documents—as well as interviews with scores of Kurdish survivors, senior Iraqi defectors, and retired U.S. intelligence officers—demonstrates that Iraq carried out the attack on Halabja, and that the United States, fully aware of this, nevertheless accused Iran, Iraq's enemy in a fierce war, of being partly responsible for the attack. This research concluded there were numerous other gas attacks, unquestionably perpetrated against the Kurds by the Iraqi armed forces. In 2001, Jean Pascal Zanders of the Stockholm International Peace Research Institute (SIPRI)'s Chemical and Biological Warfare Project also dismissed the allegations, arguing that "The coloring of the victims is more suggestive of sarin, which was in Iraq's arsenal." Leo Casey, writing in "Dissent Magazine" in 2003, observed that Pelletiere's analysis was based solely on images and testimony of blue discolorations and ignored all other evidence—including the recollections of hundreds of Kurdish witnesses; academic studies based on medical examinations, soil samples, and autopsies; and captured Iraqi government documents—proving Iraqi culpability.