Complex sentence: The IDF also dismissed as "unimportant" evidence gathered by Human Rights Watch indicating that the IDF's suggested timeline surrounding the fatal incident is flawed, which thee IDF originally claimed was the most important factor absolving it of responsibility.
Split into simpler sentences: The IDF also dismissed as "unimportant" evidence gathered by Human Rights Watch indicating that the IDF's suggested timeline surrounding the fatal incident is flawed. Yet, the IDF originally claimed that the timing of the incident was the most important factor absolving it of responsibility.