The Criminal Superman

Superman...a criminal?  Say it ain't so!

Yet, here he is...accused of killing Lex Luthor.

How did the heroic Superman find himself in this situation?

Action Comics #318 (November, 1964)

Starting off with "The Death Of Luthor!" by Edmond Hamilton, Curt Swan and George Klein.  To be fair, it starts on Earth, where prisoner Lex Luthor escapes prison...and heads to a rocket launch, to end up on the planet Lexor, where Luthor is considered a hero, and is under a red sun. While there, he marries a native woman, Ardora, whom he had known before.  

Superman, getting a spaceship to follow Luthor, does, ending up on Lexor (where the red sun makes him powerless). There, after chasing down Luthor, the two fight...with Superman seemingly killing Luthor.  The local establishment take Superman into custody, where he is to be tried for murder.

Action Comics #319 (December, 1964)

Picking up where the last issue left off, "The Condemned Superman!" by Edmond Hamilton, Curt Swan and George Klein.  On trial, it goes badly for Superman.  Superman escapes jail before a verdict is rendered, with the man of steel finding one of Luthor's secret laboratories, therein he finds proof of a formula that Luthor invented that a person could take to simulate death.  

Going on that theory, Superman tries to revive Luthor...and is successful.  Luthor faked his death to get the authorities to sentence Superman to death.  Though this clears Superman, the Lexorians do not believe Luthor to be guilty.  Superman leaves Lexor, banished, while Luthor stays there with his new wife.