What actually is a smoking gun?

A smoking gun is a clue that shows you who the villain was. As opposed to clues that only imply who the villain might be. If someone is caught holding a gun that is still smoking you are pretty sure he fired the shot even though nobody saw him shoot it.

The front of the car has a dent and has the victims blood all over it. This is the smoking gun we were looking for.

Smoking Gun TV

in the old days when a gun fired...it would smoke. Thr trail of smoke would make it obvious that the gun went off...a clue to retrace a crime! Think of the opening to the tv western Gunsmoke...Marshall Dillon draws down and fires his 6-shooter. Off the barrel, there would be a white smoke come up. Hence, a smoking gun!

Let me put it in terms you will understand. Don't get mad at me I'm just using this as an example for you to understand the answer. You know them sticky socks you mom found in your room after you...well ...you know.....those sticky socks are the smoking gun, proving that you were.....well .....you know. I'm not saying you did that, I'm just making a clear example of what it means. The other answers were not very good examples.

The Main Evidence that Can point the Guilty finger is the Somking Gun.

Got it?

The undeniable proof in a crime.

Once you have the smoking gun you it's easy to pin down a suspect in a court of law.

literally means a gun that has just been fired.

"That kid is a smoking gun," means that he is guilty.

read a book

a smoking gun is one that has just been fired

the smoke being clear evidence of that

with that understanding, surely you can see how one might apply that metaphorically to other situations

It means getting caught.

clue that will come back to haunt you