Johnny Allen Johnson was born on March 16, 1978, in the state of Missouri, United States. He had a difficult history marked by mental health diagnoses, including schizoaffective disorder, and a prior conviction for burglary before his involvement in the 2002 murder of 6-year-old Cassandra “Casey” Williamson.

In early 2002, Johnson had recently been released from a state psychiatric facility where he had been institutionalized for schizophrenia. Despite ongoing mental health concerns and treatment lapses, he maintained close ties with the Williamson family, especially through his sister's childhood friendship with Casey's mother.

On July 26, 2002, in Valley Park, Missouri, a six-year-old girl named Casey Williamson was abducted from her home. Witnesses reported seeing her being taken by a man later identified as Johnny Allen Johnson, a family acquaintance. After an extensive search, Casey's body was discovered near an abandoned glass factory less than a mile from her home.

Authorities arrested Johnson after he confessed to the murder. He revealed that he had taken Casey to the factory with the intent to rape her. When she resisted, he assaulted her multiple times with a brick and a large rock, which ultimately led to her death. Following the murder, Johnson disposed of her body in a pit and washed himself in a nearby river.

A memorial service was held for Casey on July 30, 2002, where many community members gathered to pay their respects. The investigation led to Johnson being charged with multiple crimes, including first-degree murder, armed criminal action, kidnapping, and attempted rape. His trial began in 2005, where he acknowledged his guilt but claimed diminished responsibility due to mental illness. His defense argued that he was suffering from schizoaffective disorder at the time of the crime.

The court found Johnson guilty, and he was sentenced to death on March 7, 2005. Over the years, he attempted several appeals to avoid execution, citing his mental health issues. However, these appeals were consistently denied. On April 20, 2023, the Missouri Supreme Court set an execution date for Johnson.

Despite last-minute efforts for clemency and further appeals citing his mental condition, Johnson was executed by lethal injection on August 1, 2023. His final meal consisted of a bacon cheeseburger, curly fries, and a strawberry shake. In his last statement, he expressed remorse for his actions.