Authorities say the couple was overpowered, tied to an anchor and thrown overboard off Newport Beach in 2002. The Hawks apparently thought the defendants were prospective buyers and were taking them on a test run of the yacht.
The last of four defendants in the case was sentenced earlier this week.
Alonso Machain, 25, was sentenced to 20 years behind bars. Earlier, Long Beach residents Skylar Deleon, 29, and John Fitzgerald Kennedy, 43, received death penalties, and DeLeon's former wife, Jennifer Henderson got a sentence of life in prison without parole
The bodies of the Prescott, Arizona couple have not been found. The yacht had been kept in storage as evidence during the murder trial.