Ok...let's go hypothetical nurse... and I am a critical care nurse...worked regional level one burn unit, open heart, sicu, nicu, etc for the last 15 years... anyhoo. if the stain is dormant in a rug or in a place that would allow for seepage...ie, already dead or died in the same spot. If there is no spatter or transfer (which we have not heard about...but doesn't mean it didn't or doesn't exist) you can assume that whatever left a stain that was picked up on by black light in the trunk had oozed onto the area it stained...and that is passive...not active...staining IMHOO. We do not know how big or small the stain was.... if there were someone deceased placed in the trunk...even wrapped in a blanket....upon my knowledge of what happens after death and amount of bodily fluids that can accumulate, it is possible to even soak through blankets and leave a miniscule stain and an area that cadaver dogs could pick up on...again....my professional opinion only and sorry if it was too graphic.
~nurse unplugged