No.
Were there witnesses to the crime?
No.
was the murder premeditated?
No.
Was the murderer an employee (or owner) of the store?
Yes.
Ok: theory number one.
Donald is at a pet store. He gets mad for whatever reason, and threatens to sue/shut down the store. The clerk on duty, angered or what have you, has one of the animals attack him and kill him. The animal is cleaned, put back as if nothing happened, and is never recovered as a murder weapon.
No.
Were any aspects of that theory correct? (the setting, the method, the perpetrator)
This question and answer is really bugging me, not because I asnwered it wrong, but because it might be a bit misleading. Let me reword the question and answer like this:
At the time of the murder, did the murder weapon belong to the animal, plant or fungus kindgom (as opposed to a rock or the like)? Yes.
I am not saying any more than that.
Was he killed in such a way as to leave an externally visible mark?
Followup question: if yes, was the mark left as an indicator of damage (a gash, bruise, etc. as opposed to a rash or discoloration)
That is part of problem of longer answers and being limited to only a few answers. You know that it was an employee or owner, but that isn't the entire "who" aspect.
This part is correct.
Yes.
Ok, then. Expounding on the perpetrator.
Was he (ignoring gender differentiation. I assume that's not relevant, for now.) a janitor?
No.
When you say animal kingdom, do you mean human?
No.
phrased more concisely, was the "murder weapon" a non-human animal?
Define what you mean by "animal"?