Brian James Dugan was born on September 23, 1956, in Nashua, New Hampshire. He was the second child in his family, which included one sister and three brothers. Brian's parents, James and Genevieve Dugan, were both alcoholics. This troubled family environment had an impact on Brian's early life. In 1967, when he was about 11 years old, the Dugan family moved to Lisle, Illinois.

Dugan's birth was described as traumatic. According to his family, he began to emerge before the doctor arrived. A nurse and an intern allegedly pushed his head back inside his mother and strapped her legs together in an effort to delay the birth. Family members later expressed concerns that this incident might have caused brain damage. As a child, Brian suffered from severe headaches followed by vomiting, for which he took medication until he was a teenager. He was also a chronic bed wetter, similar to his father.

From a young age, Brian displayed behaviors that would later be recognized as signs of psychopathy. He was seen by child specialists, but they did not understand these symptoms. At age 8, he and one of his younger brothers set the family garage on fire. When he was 13, Brian poured gasoline on a cat and lit it on fire. In 1972, he ran away to Iowa, and later that year, he faced his first arrest for burglary. Over the years, he was convicted of various crimes, including arson and battery.

Brian's relationships with his family were strained. His younger brother, Steven, reported that Brian attempted to molest him after a stay in a youth home, where Steven suspected Brian might have been sexually assaulted himself. In 1974, Dugan tried to abduct a young girl from a train station, but the charges were later dropped. The following year, he threatened his older sister, Hilary, and vandalized her car. Steven also mentioned that Brian complained about being sexually abused while he was incarcerated at the Menard Correctional Center from 1979 until 1982.

On February 25, 1983, Brian Dugan abducted 10-year-old Jeanine Nicarico from her home in Naperville, Illinois. She was home alone that day and was found missing after two days. Her body was located six miles from her house, and it was discovered that she had been raped and beaten to death.

Dugan's next known victim was 27-year-old Donna Schnorr, whom he attacked on July 15, 1984. He followed her in his car and ran her off the road. Once he got her out of her vehicle, he beat and raped her. Dugan then drowned her in a quarry.

In 1985, Dugan committed a series of crimes leading up to the rape and murder of eight-year-old Melissa Ackerman. On June 2, 1985, Melissa and her friend Opal Horton were riding bikes in Somonauk, Illinois. Dugan confronted them and initially grabbed Opal, but she managed to escape. Dugan then overpowered Melissa, raped her, and killed her by drowning her in a creek over 15 miles away. Melissa's body was not found for several weeks.

Dugan was arrested the day after Melissa disappeared. He had attracted police attention for an expired vehicle inspection sticker. After the discovery of Melissa's body, evidence linked him to the crimes. Dugan later pleaded guilty to the murders of both Donna Schnorr and Melissa Ackerman to avoid the death penalty. He was sentenced to two life terms in prison.

Later, while in custody, Dugan provided an unofficial confession regarding the murder of Jeanine Nicarico. He had not been a suspect in her case initially, but his DNA matched evidence collected from the scene. In 2005, he was indicted for Jeanine's murder. Dugan pleaded guilty in 2009 and was sentenced to death. However, after a law to abolish the death penalty in Illinois passed in 2011, his sentence was commuted to life in prison. He is currently serving his sentence at the Stateville Correctional Center.