I don't know if you're reading the reviews on TtH, but I can tell you're reading them here. :) The review I left on TtH has some links you probably should look at, because it concerns what the police might find when they test that blood, and compare it to Dawn's. :) Exactly what they find is up to you, of course, but we'd been doing some fanwanking on what conclusions they might draw from various scenarios.
Blood Test
*** Ponder