One prominent hypothesis about illnesses among Gulf War veterans is that some reported symptoms may have resulted from exposure to chemical warfare agents. During and after the Gulf War, some veterans reported they had been exposed to chemical warfare agents. To investigate these incidents and assess the likelihood of chemical warfare agents' presence in the Gulf, the Department of Defense developed a methodology for investigation and validation based on work of the United Nations and international community. The investigation examines these factors:

While our investigative methodology (more fully described in Tab C) is based on these factors, the passage of time since the Gulf War makes it difficult to obtain certain types of documentary evidence, and physical evidence often was not collected when an event occurred. Therefore, we cannot apply a rigid template to all incidents, and must tailor each investigation to its unique circumstances. Accordingly, we designed our investigative methodology to thoroughly define each incident's circumstances and determine what happened. Alarms alone are not certain evidence of chemical warfare agent presence, nor is a single observation sufficient to validate the presence of a chemical warfare agent.

Following our methodology, we accumulate anecdotal, documentary, and physical evidence; interview witnesses and key servicemembers; and analyze the results of all available information. The investigator then assesses the possibility of the presence of chemical warfare agents on the battlefield. Because we do not expect to always have conclusive evidence, we developed an assessment scale (Figure 1) ranging from Definitely Not to Definitely, with intermediate assessments of Unlikely, Indeterminate, and Likely. This assessment is our best judgment, based on facts available on the report publication date; we reassess each case over time based on new information and feedback.

Figure 1. Assessment of chemical warfare agent presence

The standard for making the assessment is based on common sense: do the available facts lead a reasonable person to conclude that chemical warfare agents were present or not? If insufficient information is available, the assessment is Indeterminate until more evidence emerges. The UK Ministry of Defence has conducted its investigation along similar lines, relying on documentary evidence and the testimony of key witnesses.

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