Brandon Howell, 39, a man with a violent past, was convicted on Monday of five counts of first degree murder and seven other crimes.
The Jackson County jury deliberated less than two hours after getting his record on Monday morning. The defense summoned no witnesses and did not present any evidence during his trial, Kansas City Star reported.
Patrick J. Berrigan and Molly Hastings, among several attorneys representing Howell, declined to comment after the verdicts.
Friends of the victims got bogged down and cried after the verdict was announced.
According to court records, the killings began when Howell attempted to rob a classic Jaguar at the home of George Taylor, 80, and his wife, Anna Taylor. Police said Howell had failed to start the car and instead stole the Taylors sport utility vehicle.
Witnesses told the police that they saw the driver of the Taylor vehicle stop in front of the neighboring house in Choucroun. He went out and shot him in his driveway before leaving. They died a week later in the hospital.
Two other potential witnesses to the robbery - 88-year-old Lorene Hurst and her 63-year-old son, Darrel Hurst - were also shot, probably as they were returning from the grocery store.
Howell had long been on the radar of the police. In 1998, the body of his classmate, 18-year-old Nick Travis, was found buried in the yard of a duplex in Kansas City, Missouri, being renovated by Howell's father.
Howell was arrested during a robbery of home invasion in Gardner, Kansas in 1999, in which a cat was beheaded. He pleaded guilty and was sentenced to 12 years in prison.