Mark Alan Smith was born on June 27, 1949, at the Illinois Masonic Hospital in Chicago. His parents were Charles Gilbert Smith, a marine, and Delores Rechlin. He was the second of five children. When Mark was about 2 or 3 years old, his parents separated. His mother gained primary custody of him and his siblings. When Mark was 7, his mother remarried, and the family moved to McHenry County, Illinois.

Growing up in McHenry County, Mark attended local schools. He had trouble adjusting to his new environment. He struggled with anger issues, which led to difficulties in school. Eventually, he returned to Chicago for a period of time. During this time, while attending Edgebrook Public School, he had a serious incident in which he attempted to strangle a female classmate behind the school building.

The following year, Mark stabbed a 6-year-old friend with a pen knife more than 20 times. The boy survived the attack, but Mark was sent to see a psychiatrist after that incident.

In 1966, at the age of 17, Mark enlisted in the Army during the Vietnam War. He was stationed in West Germany. In 1967, he was court-martialed for assaulting four members of his unit who were African American. After serving for three years, Mark returned to the United States, settling back in McHenry County.

On December 3, 1969, Mark Alan Smith kidnapped 32-year-old Obie Fay Ash. He raped and strangled her in Mountain Home, where he worked as a handyman. After confirming she was dead, he stabbed her multiple times. Smith then tied her up with wire and placed her in the backseat of her car. He drove the car close to his workplace, and Ash's body was found later that day.

On January 27, 1970, he abducted 27-year-old Jean Bianchi from a laundromat in McHenry. After forcing her into his car at knifepoint, he raped and stabbed her. Smith then dumped her body in a nearby creek. It was discovered three days later.

Next, on February 27, 1970, Smith attacked 22-year-old Janice Bolyard at the Resin Research Laboratory where they both worked. After making unwanted sexual advances, he choked her until she lost consciousness. He then raped her and strangled her with her own pantyhose. Her body was found the following day.

On May 27, 1970, he murdered 17-year-old Jean Lingenfelter. After she left her home to meet him, she was last seen entering his car. The next day, her body was found on a beach. Smith admitted to raping and strangling her, and later disposing of her body in McCollum Lake.

In addition to these murders, Smith confessed to killing several women while stationed in West Germany during his military service. Though he recanted some of those confessions, authorities believe he could be involved in more than 20 murders across multiple locations.

After the murders of Bianchi and Lingenfelter shocked the community, Smith was arrested. He was found guilty of several murders and was sentenced to 500 years in prison. He later attempted to escape custody, receiving additional time for that. Smith continues to claim that he has changed and has been denied parole multiple times. He remains incarcerated and has engaged in selling art and pursuing education while serving his sentence.