The prosecutor claims that one blood stain is covered by another to show that one person was shot before another. In real life, as the two people shot were hit within seconds of each other, their blood stains would mix together. This would make it impossible to determine who was shot first from just the blood stains.
The bloodstains in the shop are not consistent with a shotgun firing buckshot at medium range. There should be far less blood on the walls, and it should be spread in a much wider, less consistent pattern.