Who’s the killer ?

A boy and a girl are at the cinema bar waiting the movie to start. The seller woman asks them:

“Do you want popcorn ?”

“No, thanks.”

“Maybe you want cola ?”

“No.”

“Some chewing gum, then ?”

“No… no !…”

The seller woman is disappointed, turns back and wants to leave, but before she whispers:

“The killer is the driver…”