I would appreciate any help you can provide on this subject which is a major plot point of my story. I need some specifics on how forensics would determine how long ago the corpse was stashed in the wall, and how decomposed the body would be. Figure an apartment wall in an old project house in Detroit as the location. Also, a detective's gold shield is in the suit and a wedding band on the floor inside the wall. The body has five gunshot wounds.
blood below the body in the wall would indicate if the body was moved there right after the killing or if it was some time before the body was moved.
Entomology takes the life cycles of flies and other insects to help determine the amount of time a body was at a certain location. Flies will lay eggs in either the openings on the head or wounds if there are external wounds available. Decomp. of the head first and then down indicates that the body did not likely have any wounds below the neckline, if any at all. With an absence of bugs, humidity and temp. are probably the main factors in how fast it will decomp.
DNA tests will hopefully discover who the victim is, and possibly provide leads to contact loved ones and find out when the victim was last seen alive.
Investigators would look for blood to be settled in the body by gravity (lividity). Blood stops pumping and settles in the body. This happens from 30 minutes after death to 12 hours after death. This gives a ballpark of time of death. This also can indicate if the body was moved after resting for 6 hours or more, as lividity is only affected by movement in the first 6 hours. If a body is resting on its back, there will be purple coloration around the back side of the body, except for where the back is actually in contact with the floor (this is lighter colored because pressure from the floor is keeping blood out of those blood vessels. This can also indicate if anything was under the body at any point from 6-12 hours after death that is no long there, or if the body was moved in that time frame.
Investigators will also look for receipts for drywall or anything used to hide the body. Obviously, this will give a better time frame.