Who killed 1,000 shinobi?

Could you please elaborate on the circumstances surrounding the death of 1,000 shinobi? Were they all killed in a single event, or over a period of time? Was it an act of war, an assassination, or perhaps a tragic accident? Was there any evidence left behind, such as weapons or clues that could lead to the perpetrator? And finally, have there been any suspects identified, or is the case still under investigation? I'm eager to learn more about this tragic event and the efforts being made to uncover the truth behind it.