All depends on how the blood got there. Possibilities include:
Also, it is troubling that there is the still no convincing account of how DW got possession of the girl in the first place. There is no evidence for the theory he went into her bedroom and carried her away. No one saw him or heard him or the girl, and he left no physical evidence on the premises. If he did do it, he must have found her sleepwalking and snatched her away with no one seeing or hearing anything.
Now, possibility 2 is the most intriguing. If the real killer were her parents or someone in their circle of wild friends, then we would not need to account for the quietness of the kidnapping ... and the physical evidence against DW would have an alternative explanation. Of course, if possibility 2 is true, there is at this point, alas, about as much likelihood of bringing her killer to justice as there is of catching Jon Benet's murderer.