On July 5, 1978, Harris and his younger brother commandeered a car occupied by two 16-year-old boys, John Mayeski and Michael Baker, ordered them to drive to a remote area, then killed them.

[2][3] Kenneth was a sergeant in the United States Army who was awarded a Silver Star and Purple Heart for his service in World War II.

[2] With Kenneth in jail, the remaining family members lived a migrant life around the San Joaquin Valley.

On July 2, Daniel stole two guns from a neighbor's house in Visalia, California, and the two drove to San Diego that night.

[5] On July 5, the Harris brothers happened upon John Mayeski and Michael Baker, both 16, sitting in a green Ford LTD eating cheeseburgers in a supermarket parking lot in Mira Mesa.

[8] About an hour later, the Harris brothers robbed the Mira Mesa branch of the San Diego Trust and Savings Bank located across the street from where they had abducted Mayeski and Baker, and fled with about $2,000.

An appeal for clemency to California governor Pete Wilson – who was mayor of San Diego at the time of the killings – was rejected in a live television news conference, where Wilson read a statement acknowledging Harris' abusive childhood but ended with a clear rejection of the clemency request, saying, "As great as is my compassion for Robert Harris the child, I cannot excuse or forgive the choice made by Robert Harris the man.

[13] In 1990, federal appeals court judge John T. Noonan Jr. issued a stay of execution, as Harris argued that childhood brain damage interfered with his judgment during his crimes.

[15] On April 18, U.S. District Judge Marilyn Hall Patel issued a temporary restraining order barring Harris' execution while she considered his lawsuit challenging the gas chamber's constitutionality.

[15][16] On April 20, the U.S. Supreme Court had vacated a separate stay of execution the Ninth Circuit had issued on Harris' habeas corpus petition.

Later that evening, the Ninth Circuit entered a third stay blocking the execution while it reconsidered reimposing the lower court's temporary restraining order.

[15] That night, the U.S. Supreme Court issued a per curiam decision vacating the Ninth Circuit's stays and allowing the execution to proceed, by a vote of 7–2.

For his last meal, he had requested and was given a 21-piece bucket of Kentucky Fried Chicken, two large Domino's pizzas, a bag of jelly beans, a six-pack of Pepsi, and a pack of Camel cigarettes.

[18] The execution is specifically remembered for his choice of final words (recorded by Warden Daniel Vasquez): "You can be a king or a street sweeper, but everybody dances with the grim reaper.