John Richard Marek was born on September 17, 1961, in the United States. 

On June 16, 1983, Adella Marie Simmons and Jean Trach were returning home from a holiday trip when their car broke down on Florida's Turnpike. John Richard Marek and his accomplice Raymond Dewayne Wigley stopped to help them. They convinced Adella to ride with them to a service station for assistance. Instead of taking her to safety, Marek and Wigley drove her about 60 miles away to a beach.

At the beach, they assaulted Adella multiple times. Afterward, they strangled her using a bandana and then set her body on fire. Both Marek and Wigley were later captured and faced trial for their crimes.

During his time in prison, Marek's accomplice Raymond Wigley was killed by another inmate in 2000.

John Marek was sentenced to death for his role in the murder. He had several scheduled execution dates. He was initially set to be executed on May 13, 2009. However, the execution was delayed. The Florida Supreme Court later lifted the stay of execution, and a new date was set for August 19, 2009.

Before the execution, Marek's attorney presented a motion claiming a new witness could prove Marek’s innocence. The judge denied this motion.

On August 19, 2009, Marek was executed by lethal injection at Florida State Prison. The execution took 13 minutes, and Marek was pronounced dead shortly after. He became the 68th inmate executed in Florida since the death penalty was reinstated in the state. His last words were a prayer.