Joseph Breslin was born on May 21, 1950, in Philadelphia. He had a troubled childhood and struggled with mental illness. During the 1960s, he spent time in two different mental institutions in Pennsylvania. While in one of these institutions in 1968, Breslin killed a fellow patient and attacked a nurse. However, these incidents were kept secret due to confidentiality rules, and the details were never made public.

In 1975, Breslin was moved to the California Men's Colony, where he met Douglas Cain, his cellmate. Two years later, Breslin shot a man in the head with a shotgun, but the victim survived. Breslin took a plea deal, reducing his charges to assault with a deadly weapon, and he served a 3-year prison sentence. After his release, he returned to San Luis Obispo.

On the night of June 23-24, 1982, Breslin went to the apartment of Linda Sue Cain, the wife of his former cellmate. Once inside, he stabbed Linda to death and strangled her 8-year-old daughter, Desiree. He moved their bodies to the bathroom and left a letter filled with incoherent ramblings, profanities, and expressed a desire to end his life. Breslin then stole Linda's car and drove towards Nevada.

In Nevada, Breslin crashed the car near Jackpot. He hitched a ride to a nearby camping area where campers helped him and called the police. A sheriff's deputy, Denny Lawrence, arrived to check on Breslin. While Lawrence was filling out an accident form, Breslin shot him in the back of the head with a concealed .22 caliber pistol. Lawrence survived but was critically injured. Breslin then took Lawrence's revolver and began shooting at the campers. Two brothers returned fire, hitting Breslin multiple times. Both Breslin and Lawrence were taken to separate hospitals, where Breslin died from his injuries on June 28, 1982. Lawrence survived but was left permanently disabled.

When authorities examined Breslin's body, they found a letter in which he expressed his desire to be dead before 1983. They discovered that the car Breslin had crashed was registered to Linda Cain, who had been murdered along with her daughter a week earlier. The similarities in the letters and Breslin's connection to the victims led authorities to close the cases, but no clear motive for his crimes was ever determined.