If they found blood in large enough quantities, that could be enough to convince me that she's dead, at least. I've seen several different cases on the "New Detectives" (Discovery Channel) where blood was found (thanks to good old Luminol) in large enough quantities that experts were convinced that no one could have survived losing that much blood.
If I were a juror, and the evidence shows he was in her bedroom, and there were large quantities of blood found in his camper, it wouldn't take much for me to convict him of murder, without a body. The threshold is "beyond a reasonable doubt". Barring a house fire, a middle-aged neighbor breaking into a 7-year old girl's bedroom is up to no good. No reasonable person would argue with that.