I totally believe that the storage building story was concocted by the Laundries after the fact. MOO:
Mommy bought BL a ticket to fly home, BL was too furious at GP to let "it" go so he went back, killed her and took the van.
BL gets home, parents don't ask questions because they don't care what happened to GP.
Dad called the lawyer, who,
(alledgedly MOO, crime is not his specialty unless it involves real estate, alledgedly MOO), says the neighbors need to see BL being a good boy with Mom and Dad in FL- far, far away from Utah. "Oh, and be sure to stall the cops! "
"No problem, we got this!" says good 'ole Mom and Pop. This ain't their first rodeo.
BL bikes with Mom and mows the lawn. (
Leave it to Beaver theme music wafts through the air.)
The whole family including sis helps BL disappear and here we are.
MOO