Lonnie David Franklin Jr. was born on August 30, 1952, in Los Angeles, California. He grew up in South Central Los Angeles. Not much is known about his early childhood or family background. As an adult, he married and had two children.

In 1975, Franklin was discharged from the United States Army with a dishonorable discharge. This was after he had served time in prison for a serious crime. In April 1974, while stationed in Stuttgart, West Germany, he was convicted of gang-raping a 17-year-old girl. The crime occurred when he and two other soldiers offered the girl a ride home and then attacked her.

After his military service, Franklin encountered more legal issues. In 1989, he was convicted of two theft charges, a misdemeanor assault charge, and a battery charge. He served time for one of the theft charges.

In the mid-1980s, authorities in Los Angeles began investigating a series of murders linked to a killer who targeted black women, particularly those who were street sex workers. These murders were initially attributed to a single killer known as the "Southside Slayer." From 1983 to late 1985, this killer was believed to have murdered at least 13 victims. As investigations continued, activists and community members criticized the police for their lack of urgency in addressing the murders of marginalized women.

By early 1986, the task force investigating the case had identified 15 murders. Despite the efforts of law enforcement and community activists, the investigation struggled to yield leads. As years passed, it became apparent that multiple serial killers may have been involved in the deaths, complicating the case further.

In the 2000s, a link between a new murder and earlier cases emerged through DNA analysis. In 2007, Janecia Peters was killed, and her death pointed back to unsolved murders dating back to 1985. This rekindled interest in the original cases, leading to the formation of a special investigation team named the 800 Task Force.

The investigation took a significant turn when Familial DNA analysis connected Lonnie Franklin Jr. to the crimes. Although Franklin's DNA had not been collected after a prior felony conviction, it was linked to DNA from the crime scenes after authorities identified a family relationship through his son’s DNA profile. In July 2010, Franklin was arrested based on this connection, facing charges of ten counts of murder and one of attempted murder.

In December 2010, after searching Franklin’s home, investigators found over 1,000 photographs of women, some of whom were believed to be potential victims. These images included both conscious and unconscious individuals taken over several decades.

Franklin was tried for his crimes starting in February 2016, and after a lengthy trial, he was found guilty in May 2016. Following his conviction, evidence came to light suggesting he might be linked to additional murders beyond those for which he was charged. In June 2016, he received a death sentence for his crimes.

Franklin died in his prison cell in March 2020, with no signs of trauma reported.