Daniel Blizzard faces a first-degree murder charge in the death of Vern Holbrook.
The realtor was found badly beaten last year in a home up for sale in Cowiche. He died months later.
Another suspect in the case will be tried separately. Prosecutors highlighted the severity of the beating.
The defense brought into question the testimony expected from witnesses who reached plea deals to testify against the defendants.
"After he was assaulted, he never got better. He was never able to speak again, never able to walk again," said Prosecuting Attorney Alvin Guzman. "He lived the rest of his life for a lack of a better word, a vegetable."
"Ask yourself what would you do if your liberty was at stake like Adriana Mendez and you have three children and you've been in jail for a year and you want to get out," said Defense Attorney Pete Mazzone.
The trial is expected to last a couple of weeks.