No, the relatives also took Sheila's bloodstained underwear with them back to their farm.
That's two possible sources.
Oh yes. The clothes in the bucket of water.
The relatives were very determined to frame an innocent man of murdering his family. Days after the massacre.
Wet clothes, silencer, blood, rifle lenght, Sheila's contact shot, the rifle nozzle not having any blood on. They had all angles covered.
I hope my family never turn on me like that.