Very odd that there is an empty casing on top of the blood pool...
Not really. It looks like the gun was kicked clear of the perp (standard procedure), during which, some shell casings were kicked as well. You can see the blood skid marks where the gun was slid away from the perp.
108 posted on 10/03/2017 7:03:20 PM PDT by BlueMondaySkipper
(Involuntarily subsidizing the parasite class since 1981)