The investigation into complex historical events like the assassination of President Juvénal Habyarimana and the Rwandan genocide can be challenging and time-consuming due to various factors. Here are a few reasons why investigations may take a long time:

1. Complexity: Investigating such events involves examining numerous sources, collecting witness testimonies, analyzing forensic evidence, and reviewing historical records. This process requires meticulous attention to detail and collaboration among different parties.

2. Access to Information: Gaining access to relevant information can be difficult, especially if some documents or individuals are unwilling or unable to cooperate with investigators. It often involves navigating through bureaucratic hurdles and addressing legal challenges.

3. Political Considerations: Investigations into politically sensitive events may face obstacles due to political pressures, conflicts of interest, or concerns over national security implications.

4. International Cooperation: International involvement in conflicts can complicate investigations as it requires coordination between multiple countries' legal systems, sharing intelligence, respecting jurisdictional boundaries, and overcoming potential diplomatic hurdles.

It's important for investigations of historical events like the Rwandan genocide to follow rigorous processes in order to bring about justice while maintaining accuracy and credibility in their findings.