5. Disease
Disease is another theory that has much historical basis to support it. The Roanoke colonists could have encountered a New World disease that they had no immunity to fight. The theory goes that the colonists could have caught a good, old-fashioned plague that presented with symptoms of delirium, paranoia, or madness. Considering the reports from Native American tribes in the area of internal warfare in the Roanoke settlement before everyone disappeared, this seems like a viable theory.
The healthy could have wanted to get rid of those who were sick because they were afraid of getting sick themselves. This easily could have escalated into a violent situation. Once the disease hit, the healthy population could have sectioned off into smaller groups and left the colony, leaving the sick to die.
That certainly could explain the multiple sightings of Europeans in local Indian populations in later years after the colony disappeared. The only problem with this particular theory would be, what happened to the bodies of the sick?