At the end of the day, if Sheila was not shot under the chin until after the police had an opportunity inside the farmhouse (downstairs) to incapacitate her, and or to prevent her from being shot further, then of course the police are responsible for her death, particularly if the second shot under the chin was inflicted or received later on in the bedroom, whilst a training exercise or fooling around with the gun and the body took place...
I know for a fact that there exists photographs of Sheila on the bed, and she only had one wound to her neck with no blood running from the corners of her mouth, so nobody needs to persuade me, or convince me what took place in so far as the fact that Sheila was shot for the second time after the firearms officers supposedly left the scene at just around 9am...