One more for the Roanoke disappearance not being much of a mystery. Sure, we aren't certain what happened but they were failing and sent to get help from England, and none came. By the time anyone did, it was 2 or 3 years later, they found the message about Croatan but didn't investigate. I think it's near to certain they ended up with the Croatan and were assimilated. Violence seems unlikely, as Thermal said, there were generally friendly and the Colonists packed up everything they owned. It wasn't all burned down and there weren't any other signs of violence. Maybe some other tribe violently attacked the Croatan though.
And smallpox. There was an epidemic around 1615 that killed up to 90% of the natives. Likely anyone who had any knowledge of what happened died.
ETA: It was contemporaneous with the Spanish Armada, it wasn't much of a priority for anyone in England either.