Kevin Spacey did it.
The film begins with Kevin Spacey's character being questioned by police and ends with him doing it. Along the way he lies about doing it, but we soon find out that he does, in fact, do it, and we are amazed that we didn't see how he couldn't have done it earlier, but now that we see it, we see that, yes, he did, in fact, do it.
Then there's a boat and some people getting fucking shot and the guy that wrote "A Bronx Tale" drops a coffee mug.
Kevin Spacey: ("Verbal" Kint) He does it.
Chaz Palminteri: (Special Agent Dave Kujan) He interviews Spacey and finds out he did it. Before Palminteri accepted the role, it was offered to Christopher Walken, Robert DeNiro, and Al Pacino. Since Marlon Brando was too fat at the time, Paul Newman didn't give a shit, and Lawrence Olivier was goddamn dead, the filmmakers decided to go with Palminteri.
Stephen Baldwin: (Michael McManus) Before gaining fame as "that one Baldwin brother that isn't fat", Baldwin was offered the role of McManus, and then went on to get slightly fat, bankrupt, and appear on "I'm a Celebrity... Get Me Out of Here." He also loves Jesus.
Kevin Pollak: (Todd Hockney) Pollak audtioned. He got a job. Have you seen his Shatner impression?
Benicio Del Toro: (Fred Fenster) Del Toro plays a mush-mouthed, English Language-ripping latino named... Fred. The part was originally written for Harry Dean Stanton. Seriously.
Gabriel Byrne: (Dean Keaton) Byrne initially turned down a part in the film simply because he read the script and didn't see how the filmmakers could pull off Kevin Spacey doing it. After some convincing, he agreed to shoot the film and Kevin Spacey went on to do it.
The film received mostly positive reviews and has gone on to be recognized as one of the greatest mystery movies of all time. The American Film Institute (AFI) ranks it as number 10 on its list of cinema's greatest mysteries for those of us who couldn't tell that Kevin Spacey did it.