Mark David Chapman killed Beatles superstar John Lennon on December 8, 1980.

Less than a year later, Chapman was sentenced to 20 years to life on August 24, 1981.

At first, Chapman pleaded not guilty by reason of insanity.  Eventually, he changed his plea to guilty.

The guilty plea allowed Chapman to cut down the length of his sentence.  The maximum was 25 years to life.  As a result, Lennon's killer first became eligible for parole in 2000.  Since then, he has come up for parole every two years.

That has forced Lennon's widow, Yoko Ono, to publicly fight against his release.  She believes that Chapman would be a threat to her and Lennon's two sons.