Paul Bernardo was born on August 27, 1964, in Scarborough, Ontario. He was the youngest of three children. His father, Kenneth Bernardo, was abusive and later convicted of voyeurism and pedophilia. His mother, Marilyn, suffered from depression and agoraphobia, eventually isolating herself in the basement. Despite his troubled home life, Paul appeared to be a well-adjusted and happy child. He was active in the Boy Scouts and maintained a cheerful demeanor. However, he harbored dark thoughts, one of which involved creating a "virgin farm" where he would breed virgin girls to rape.

At age 16, Paul learned from his mother that he was the result of an extramarital affair. This revelation led to a significant decline in his behavior and increased hostility towards his mother. He began to exhibit more aggressive and controlling tendencies. Paul attended Sir Wilfrid Laurier Collegiate Institute and later the University of Toronto Scarborough. During this time, he developed a reputation for being charming yet manipulative. His relationships were marked by emotional and physical abuse. In 1987, Paul met Karla Homolka, and they quickly bonded over shared interests in sadistic behavior.

Between 1987 and 1990, Bernardo committed increasingly violent attacks in and around Scarborough, primarily targeting his victims after following them off buses late at night. Notable incidents included the assault of a 21-year-old woman in front of her parents' house on May 4, 1987, and the assault of a 19-year-old woman in the backyard of her parents' house on May 14, 1987. On July 17, 1987, he attempted to assault a young woman but abandoned the attack when she resisted. 

Another attempted assault occurred on September 29, 1987, when he broke into a 15-year-old girl's house and attacked her in her bedroom; he fled when the victim's mother intervened. The assaults continued with the attack of a 15-year-old girl on December 16, 1987, which prompted police warnings to women traveling alone at night. On December 23, 1987, Bernardo assaulted a 17-year-old girl, earning the moniker Scarborough Rapist.

Further attacks included the assault of a 17-year-old girl on April 18, 1988, and a near capture by police on May 25, 1988, after he was seen hiding near a bus shelter. On May 30, 1988, he assaulted an 18-year-old woman in Mississauga, Ontario. He continued his spree with an attempted assault on October 4, 1988, where the victim managed to fend him off. On November 16, 1988, he assaulted an 18-year-old woman in her backyard, prompting the formation of a task force the following day. 

More incidents occurred on December 27, 1988, June 20, 1989, August 15, 1989, November 21, 1989, and December 22, 1989, each involving violent attacks on young women. On May 26, 1990, a detailed composite sketch was released by police following an assault, and by July 1990, police interviewed Bernardo after receiving tips that he resembled the Scarborough Rapist composite.

From May to September 1990, Toronto police submitted more than 130 suspects' samples for DNA testing. Investigators received two tips pointing to Bernardo: one from a bank employee in June and another from Tina Smirnis, wife of one of Bernardo's close friends. Smirnis informed detectives that Bernardo had been questioned in a previous investigation but had never been interviewed.

Police interviewed Bernardo on November 20, 1990. He voluntarily provided DNA samples and admitted that he resembled the composite. Despite this, detectives found Bernardo more credible than Smirnis. By 1990, Bernardo lost his job as an accountant and spent significant time with Karla Homolka's family. He became obsessed with her younger sister, Tammy. Karla assisted Bernardo in accessing Tammy's room and facilitated her assault by drugging her. Tammy died after the assault, and her death was ruled accidental.

On June 15, 1991, Bernardo and Homolka kidnapped 14-year-old Leslie Mahaffy. They tortured and abused her, eventually killing and dismembering her. Her remains were found in cement blocks in Lake Gibson on the day of Bernardo and Homolka's wedding. On April 16, 1992, Bernardo and Homolka abducted 15-year-old Kristen French. They held her for three days, during which they tortured and abused her before killing her. French's body was found on April 30, 1992.

Bernardo is suspected in several other assaults and disappearances, including the murder of Elizabeth Bain in 1990. He was linked to various other attacks, including the abduction and assault of a girl in 1991 and a possible involvement in a similar case in Hawaii. Despite being questioned multiple times, Bernardo evaded capture until 1993. His DNA sample, submitted in 1990, matched the Scarborough Rapist's profile in 1993, leading to his arrest. Homolka cooperated with authorities in exchange for a plea deal, revealing Bernardo's involvement in multiple crimes.

Bernardo was convicted in 1995 for the murders of French and Mahaffy, along with other offenses. He was sentenced to life imprisonment without parole for at least twenty-five years and was designated a dangerous offender. Despite various appeals and parole applications, Bernardo remains incarcerated, having admitted to additional assaults while in prison.