What's all this blood business?I don't remember hearing anything about blood.
ETA: Whoops. See everyone else is wondering too.
The point he is making is there was no blood in the trunk. There would have been if a decomposing body was in there.
Bacterial action destroys the structure of cells and soft tissues, releasing in the process body fluids in internal cavities such as chest, abdomen, and oral tract. Anaerobic microorganisms produce methane, hydrogen sulphide, and other gases responsible for the increasing stench that surrounds rotting organic matter. As gases accumulate inside the body, it starts to swell, forcing more fluids from organs to internal cavities and blood to the periphery of the body. This phase of decomposition is called the gaseous period.
And a link as requested

http://www.enotes.com/forensic-science/decomposition