Vender Lee Duncan was born on February 18, 1928, in Sinclair City, Texas. This town is located in Smith County. He had a difficult childhood and often got into fights. At the age of 17, he lost an eye, which impacted his life significantly. Eventually, he faced serious legal trouble. He was convicted of attempted murder after stabbing a man 24 times.

Later in his life, Duncan moved to San Francisco with his common-law wife, Helen Green. In San Francisco, he worked as a house painter to support himself. However, this job did not provide enough money, so he turned to burglary. He often targeted the homes of elderly people, where he committed crimes that caused great harm.

On January 9, 1955, Vender Lee Duncan entered the home of 82-year-old Marceline Herdlick through a window after climbing a fire escape. He attacked her while she was counting money, hitting her in the face and then choking her to death. After confirming she was dead, Duncan searched the apartment for valuables. He left the scene, accidentally dropping a small desk radio on his way out. Herdlick's body was discovered the next day after her landlady was unable to open the door. An autopsy revealed the cause of death was strangulation.

On September 4, Duncan targeted another elderly woman, 75-year-old Elizabeth Manning. He broke into her first-floor apartment through an unlocked window and violently beat her. After rifling through the apartment, he left, attempting to cover up the scene. The next day, concerns from her neighbors led to the discovery of Manning's body, which confirmed she had died from a violent attack. Investigators linked her murder to Duncan's earlier crime against Herdlick.

On April 5, 1957, Duncan attacked 68-year-old Ada Romig in a vacant lot. He beat her severely, causing life-threatening injuries, and dragged her body to another location. Romig was still alive when she was discovered and taken to the hospital, but she died six days later. During her time in the hospital, she was able to provide a partial description of her assailant, hinting at his age and appearance.

Just three days after Romig's attack, Duncan assaulted 73-year-old Agnes Provost. He forced his way into her apartment, attempted to rape her, but she managed to scare him off by mentioning a nearby police station. After Duncan fled, Provost reported the attack to the police and gave a clear description of him.

Duncan was later arrested for attempting to burglarize a house. While in custody, he confessed to the murders of the elderly women. He provided specific details about each crime that only the perpetrator would know. His confession indicated that he was often under the influence of alcohol at the time of the attacks, and he admitted that he resorted to killing because he couldn't stand the victims' screams.

His trial began on April 15, 1958. Initially, he pleaded not guilty and claimed insanity. However, the jury found him guilty of the two murders. He was sentenced to death and attempted to appeal his sentence, but both the California Supreme Court and the governor denied his requests for clemency. Duncan was executed in the gas chamber at San Quentin State Prison on May 29, 1959.