Cmdr. Robb Lamoureux of the Marysville police said the man's home in Brookside mobile recreational vehicle park was ransacked and his pickup truck was missing.
The pickup, described as a champagne-colored 2006 Chevrolet Colorado, was later found along an Arlington street. It had been set on fire. The fire was extinguished and the vehicle was impounded.
Police did not immediately identify the victim or discuss how long he had been dead. Lamoureux said late Friday he could not provide information on the sex offenses since that would provide identifying information.
The Snohomish County medical examiner's office said it might release the man's name by Monday.
Officers were dispatched to the man's RV at about 3 a.m. Friday after a grandson stopped by and found the man dead. The grandson told his mother, and she called 911.
Police determined the death was a homicide and launched an investigation. Detectives later asked for the public's help in locating the man's stolen pickup.
But at 10:45 p.m. Friday, crews responding to a report of a fire in the 24300 block of 19th Avenue in Arlington found the pickup in flames. Investigators determined that it had been deliberately set on fire.