Michael Duane Zack III was born on December 14, 1968, in Tallahassee, Florida. He was born prematurely after his mother was involved in a car accident. It was reported that his mother abused alcohol during her pregnancy. Zack's biological father was a soldier who left the family when Zack was young. His mother then remarried another soldier. Unfortunately, Zack's stepfather was abusive towards him and his sisters.

Zack's stepfather inflicted severe physical and emotional abuse on him. He would hit Zack, use an electric blanket to electrocute him, and force him to wear urine-soaked sheets around his neck. There were instances where Zack was slammed against the wall, kicked, and even had heated objects pressed against him. He endured many threats of violence, and at the age of three, he was hospitalized after being given alcohol and drugs by his stepfather. The abuse included attempts to drown him and poison him, and at times, Zack's stepfather even sexually abused him.

When Zack turned 11, he experienced a traumatic event that would change his life forever. He witnessed his mother being murdered by his 16-year-old stepsister with an axe. This event had a lasting impact on Zack, and after his mother’s death, he was placed into foster care.

As Zack grew older, he faced many challenges. He became involved in minor crimes as an adult. He committed offenses such as theft and property-related crimes in various states, including Florida, Texas, Oklahoma, and Tennessee. His first arrest occurred in December 1994 due to theft and probation violation in Volusia County, Florida. Later, Zack spent eight months in jail before being released in May 1996.

For nine days in June 1996, Michael Duane Zack III committed several crimes, including the murders of two women in the Florida Panhandle, shortly after his release from prison. The first murder occurred on June 13, 1996, when Zack met 40-year-old Laurie Russillo at a bar on Okaloosa Island. After befriending her, he invited her to the beach to use drugs. Once there, Zack attacked her. He beat her both in the vehicle and after dragging her out into the dunes. He eventually strangled her to death and buried her partially in sand.

The following day, on June 14, 1996, Zack met his second victim, 31-year-old Ravonne Smith, at a bar in Pensacola Beach. After spending time at the beach, Smith invited Zack to her home. Inside, Zack violently attacked her, smashing her head with a bottle and stabbing her multiple times with an oyster knife after raping her. After the murder, Zack stole items from her home and attempted to pawn them, but when the pawn shop became suspicious, he fled.

Zack was arrested three days later in Panama City. He confessed to the murders of both women. He was charged first for Smith's murder on June 18, 1996, and later faced charges for Russillo's murder. During his trials, Zack claimed that his actions were influenced by his mental health issues, which included fetal alcohol syndrome. However, the prosecution characterized him as a calculated predator who targeted vulnerable individuals in bars.

On September 15, 1997, after a week-long trial, a jury found Zack guilty of all charges, including murder, robbery, and sexual assault. The jury recommended the death penalty for the murder of Ravonne Smith, while Zack later pled guilty to the murder of Laurie Russillo and received a life sentence without parole for that crime.

Zack was put on death row and spent years appealing his sentence. His appeals were ultimately denied, and he continued to seek clemency based on his mental health claims. After a series of legal maneuvers, Michael Zack was executed by lethal injection on October 3, 2023.