Complex sentence: This involved the challenging tasks of gathering, verifying, and presenting in court eyewitness and documentary evidence of decades-old crimes that was incomplete and scattered around the world with much of it then in Eastern Europe, behind the Iron Curtain.
Split into simpler sentences: This involved the challenging tasks for decades-old crimes of gathering, verifying, and presenting in court eyewitness and documentary evidence that was incomplete and scattered around the world. Much of this evidence was then in Eastern Europe, behind the Iron Curtain.