David Russell Hosier was born on February 10, 1955, in Indiana, USA. He was the son of Glen and Martha Hosier. Glen, his father, served in the Navy during World War II and later worked as a policeman in Logansport City. In 1955, he joined the Indiana State Police. Tragically, Glen was killed in the line of duty in April 1971 by a murder suspect. This event had a significant impact on Hosier, who was close to his father. Glen and David shared many activities, such as hunting, camping, and taking rides together. After Glen's death, Martha, Hosier's mother, was overwhelmed with grief and did not give much attention to her three children.

Following his father's death, David Hosier attended military school. During this time, he faced social isolation, which further affected his early life. At the age of 19, he joined the U.S. Navy. He served for six years and worked in a naval communications unit, where he had Top Secret clearance. After leaving the Navy, he received an honorable discharge and began working as a firefighter in Jefferson City.

David Hosier was married twice in his life. He married his first wife before joining the Navy, but they divorced before he was discharged. In 1980, he remarried and had a son and a daughter with his second wife. This marriage ended in divorce in 1987.

In 1986, Hosier's mental health began to decline. He was diagnosed with depression with psychotic features and bipolar disorder after being involuntarily admitted to a state hospital in 1987. His health issues continued, and in the late 2000s, he suffered a stroke that caused brain damage.

In 1992, Hosier was arrested for assaulting his girlfriend. He was convicted and sentenced to eight years in prison. After serving some of his time, he was released on parole in 1997.

On September 28, 2009, David Russell Hosier committed a double murder in Jefferson City, Missouri. He shot and killed his girlfriend, 45-year-old Angela Yvonne Gilpin, and her husband, 61-year-old Rodney Dean Gilpin. Prior to the murders, Hosier had a long-term affair with Angela, who was estranged from Rodney. Shortly before the incident, Angela and Rodney decided to reconcile. This reconciliation upset Hosier, leading him to break into the couple's apartment and fatally shoot both of them.

After the murders, a neighbor found the bodies and alerted the police. The investigation quickly focused on Hosier, who had sent threatening messages to Angela before her death. Records showed that she had reported Hosier for stalking. Following the crime, Hosier fled to Oklahoma. He was later arrested by Oklahoma authorities and returned to Missouri to stand trial. When he was apprehended, police discovered about 15 guns in his car, including the suspected murder weapon, a STEN submachine gun. They also found a note detailing his plans for revenge against Angela.

Hosier was charged with two counts of first-degree murder and pleaded not guilty. The prosecution sought the death penalty, which is the maximum sentence for murder in Missouri. His trial began in October 2013. Hosier was found guilty of the first-degree murder of Angela and received a death sentence, along with additional prison terms for other charges. The charge related to Rodney was dismissed for unclear reasons.

Over the following years, Hosier made several attempts to appeal his conviction and sentence, but all were rejected, including by the Missouri and U.S. Supreme Courts. On February 14, 2024, the Missouri Supreme Court set his execution date for June 11, 2024. In the time leading up to his execution, Hosier's health declined, and he was hospitalized for heart problems. He petitioned for clemency, citing his past trauma and military service, but the governor denied his request.

On June 11, 2024, Hosier was executed by lethal injection. In his final statement, he maintained his innocence but expressed love for his family.