How to correctly describe in English the insufficiency of evidence presented by only one fact? I am especially interested in the possibility of using the adverb merely here.
A: But he was also at the store at the time of the holdup, so he is also a criminal.
B: How do you know that?
A: He was also at the store at that moment!
B: You are being illogical.
A: Why on earth am I being illogical?
B: That's just crazy! I mean, merely the fact that he was at the store at that moment does not mean that he was also one of the robbers!