Questioning the evidence is not the same as speculating that it could possibly have been planted or altered.
Yes, but when we say evidence shows that, for example, a rifle belonging to Oswald was found in the building they dismiss it as speculation. It's speculation that the rifle belonged to Oswald et cetera. We show the evidence, e.g., paper trail, photos, prints on it, for this and they again reply "Speculation, speculation, speculation."
The two sides may use the same words, terms, ideas but they have a fundamentally different idea as to what they mean and how to apply them.