In this case the killer is also the investigator. "So I asked the store owner if he sold me the knife (wink), he didn't hear my question (wink), and so I guess

In this case the killer is also the investigator. "So I asked the store owner if he sold me the knife (wink), he didn't hear my question (wink), and so I guess I have no choice but to close this investigation. No more questions."