Very strange. It could simply be that they ran off the road, even on I-95 or any major interstate. I was driving through SC once and looked over into a wooded area and saw a tractor trailer that had plunged into the woods and was barely visible behind a screen of trees. Turned out the driver had fallen asleep and the truck had simply gone in a straight line while the highway curved. Fortunately, it was a forest of young trees and the truck had just carved itself a path and he was not seriously injured. But the point is that even on an interstate, things can happen. People go into retention ponds all the time down here in Florida, and they are often not found for quite some time.
However, it would be interesting to know how valuable the coin collection was and who knew about it in advance.
You were prescient, livius. They ran off 95 into a swamp. What a horrible Christmas for the family.