construct specialized teams to deal with the multifaceted issues that emerge in the investigation of complex crimes. 2. Considerations relating to evidence Documentation retrieval and analysis is a vital part of investigating system crimes. For example, analysis of logistical, communications, operational, munitions, reporting and disciplinary practices can lead to strong evidence of general control, and make it increasingly difficult to rebut the conclusion that those high in the chain of command authorized the crimes under investigation.28 Depending on the circumstances, documentary investigations require creativity and subtlety, and may require proactive measures to stop those under investigation from subverting the process. Prosecutorial initiatives are often seen as urgent because evidence may be lost, destroyed or weakened with the passage of time. However, this depends on the type of evidence. It is highly unlikely that all witnesses in proceedings on large-scale and systematic human rights violations will suffer faded recollection, and there are usually plenty of available witnesses (as opposed to eyewitnesses, who can be scarce).29 Similarly, the degradation of physical evidence (such as human remains), while undesirable, may not significantly damage its evidential use. Exhumations are generally not required to determine that crimes occurred, or to identify victims, but they are helpful in demonstrating the immediate circumstances of the victims’ deaths and may give credible indications (in the case of genocide) that victims belonged to a particular social or ethnic group. Even several years between the event and the investigation generally will not degrade the evidence to the extent that it cannot be used for this purpose. (There are many other considerations governing exhumations that are significant but beyond the scope of this tool.) However, the greater risk lies with intentional contamination or destruction. Clandestine graves may be disturbed by relatives looking for the remains of their loved ones or by those seeking to pervert the course of investigations. This can create serious difficulties for the admissibility of any evidence from a particular site. The need for urgent action should emphasize effective protection of evidential sites or documents for future investigation. Such steps may need to be taken by those who are first on the ground. Anyone with responsibilities for gathering or preserving evidence should be given adequate training and should follow pre-established pro28 S ee Williams J. Fenrick (Senior Legal Adviser of the Office of the Prosecutor at ICTY), “Attacking the enemy civilian as a punishable offense”, Duke Journal of Comparative and International Law, vol. 7, p. 539, available at www.law.duke. edu/journals/djcil/articles/djcil7p539.htm. Strongly recommended is section VIII on proving offences to give a sense of the complexity of the investigation in which ordinary criminal investigators normally will have no experience. 29 In cases of system crimes, witnesses willing to testify to the general events may be plentiful, although eyewitnesses remain rare (usually many are dead or missing). In general, inconsistencies in prior statements or allegations that the witness suffers from post-traumatic stress disorder will not be fatal to the testimony. 14