From what I have read the blood found in the silencer was Sheila Caffell's blood and the only way it could have been found there was if the silencer was on the rifle and in close proximity to her when she was shot.
Just to clarify the mechanism whereby blood enters a muzzle from a contact gunshot wound is known as 'drawback' sometimes referred to as 'blowback'. This is different from blood entering a muzzle from a non-contact gunshot wound where the blood is in free flight.
Forensic scientists, ballistics and pathologists seem to agree when drawback does occur it involves the following:
- Large calibre firearms (small calibre used at WHF. 22)
- High velocity ammo (low velocity ammo used at WHF subsonic)
- Head wounds (SC's wounds were to the neck)
- Blood usually contains tissue and bone fragments (No evidence the blood supposedly found inside the silencer contained tissue or bone).
- Any devices fitted to muzzles eg silencer will alter the outcome making it less likely still as it changes the whole mechanism of how scientists believe the phenomenon works ie unsilenced hot discharge gasses blast out the end of the muzzle into the wound creating a vacuum which causes blood to travel against the line of fire back into the muzzle. With a silencer fitted the hot discharge gases enter an expansion chamber where they cool and release slowly through a series of baffle plates.
- No cases, tests or research anywhere involving blood entering a silencer as a result of 'drawback'.