[the Deejay]

That shell casing really has me interested. What is the signifigance of someone placing it in her bedroom?

[John Jamieson]

Maybe someone thought they could find a matching gun in the motorhome.

[small_l_libertarian]

My favorite theory (it didn't start with me, but I can't remember who thought of it) is that a cop who knew that the investigation was going the wrong way dropped it in there on purpose to "contaminate" all the evidence in there. Don't know that I believe it, but it is such a sensible theory.

Another idea was that Damon put it there with the intention of planting matching bullets, gun or something else at DW's. (That's obviously if you believe that Damon is the perp.)

[John Jamieson]

That's the same casing that was checked out of evidence for a few hours by "persons unknown".

Maybe someone told the cops that one of the big activities at Glamis was target shooting and they once saw DW going it.
They had no idea that the body would showup without holes.