Many of the investigations that the PCIJ has done involved examining not just a single corrupt act but a series of acts or anomalies. Investigating wrongdoing often entails looking for a pattern in the actions of corrupt officials or bodies. A single suspicious act can be explained as being due to something plausible, say, carelessness, inefficiency, or ignorance. But a pattern of suspicious actions is harder to account for. When gathering evidence of wrongdoing by officials, therefore, one often has to establish that a pattern of wrongful acts has been committed and to find out who is responsible for them.