When David and Linda meet with Sheriff Lowell, what do they learn?

Lowell tells David and Linda that two bodies were found in the woods near Lake Charmaine. Lowell says that they'd also found another item with the bodies and asks David to confirm that his blood type is B positive, then refuses to say why he wants to know. David will later learn that police had also found the bat that was used to attack David. Lowell asks David to go back through the details of the night of the attack. David says the last thing he remembers is slipping into the water after the attack. He was found by emergency rescue personnel on the floor of the cabin near the lake but says again that he has no memory of how he got there.