Jeffrey Jay Dillingham was born on March 6, 1973, in the United States. At the time of the crime, he was a 19-year-old video store employee living in Fort Worth, Texas. Public records and trial documents provide limited details about his upbringing or early personal life, and he had no widely documented criminal history prior to his involvement in the high-profile Koslow murder plot.

Dillingham was reportedly acquainted with 17-year-old Kristi Anne Koslow, the daughter of Jack Koslow and stepdaughter of Caren Koslow. Kristi was romantically involved with Brian Dennis Salter, who was also Dillingham’s associate. It was through this connection that Dillingham became involved in a planned attack against Kristi's parents in what authorities described as a plot motivated by greed and entitlement. Kristi offered the promise of a $1 million inheritance as incentive to the two young men. She also provided them with the home's alarm code to help them break in undetected.

Little else is publicly documented about Dillingham’s formative years, but his involvement in the murder that followed would lead to a swift conviction and his eventual execution at the age of 27.

On the morning of August 28, 1992, in Fort Worth, Texas, Caren Koslow was brutally murdered in her own home, and her husband Jack Koslow was left severely injured. The perpetrators were two 19-year-old men: Jeffrey Dillingham and Brian Dennis Salter, who had broken into the home using the alarm code provided by Kristi Koslow, Jack’s daughter and Caren’s stepdaughter.

According to prosecutors, the motive was financial: Kristi Koslow had promised Dillingham and Salter a share of her anticipated inheritance if they successfully murdered her parents. After disabling the alarm, the two men entered the Koslow residence while the couple slept. Dillingham reportedly beat the victims with a metal object, while Salter slit their throats. Caren Koslow died from her injuries, while Jack Koslow, though gravely wounded, managed to survive.

Following the attack, the assailants stole $200 in cash and a wristwatch valued at $1,600—an attempt to stage the incident as a robbery. However, evidence quickly pointed to the involvement of people known to the victims. Police arrested Dillingham on August 31, 1992. He was tried in 1993 and convicted of capital murder. While Salter accepted a plea deal in exchange for testifying against his co-defendants—receiving a life sentence with the possibility of parole after 35 years—Dillingham declined the offer and proceeded to trial.

Kristi Koslow was also convicted of capital murder in 1994. Although prosecutors sought the death penalty, the jury could not reach a unanimous decision, and she was sentenced to life imprisonment.

Jeffrey Dillingham, however, was sentenced to death and incarcerated on Texas death row, initially at the Ellis Unit and later transferred to the Allan B. Polunsky Unit. On November 1, 2000, at the age of 27, Dillingham was executed by lethal injection at the Huntsville Unit in Texas.