This isn’t analogous, unless your conclusion from investigating all the likely leads is “Well, there’s no way Mr White could have been murdered, I guess he just mysteriously beat himself to death with a lead pipe in the drawing room.”
Even this is somewhat disanalogous, since crime is something for which we have a good reference class, and you’re talking about post-hoc investigation of a known crime.
A better analogy would be a Police officer saying “We’ve caught all the known murderers, and the suspected murderers are all under close watch, I predict a murder rate of precisely zero for next year.”
MondSemmel is correct but if you don’t want to use the menu, type “> ” at the start of a new line and it will begin a quote block (you can also use >! for spoiler tags).