Lou Smit seems convinced it was a person with extremely violent tendencies that targeted JBR--he doesn't rule out the kidnapping motive--but underlying it all was an extremely disturbed and violent personality, with a criminal history. If you compare the crime to the life the Ramseys were living, someone wanted to ruin all that---on one of the happiest days of the year. IMO, jealousy more than a personal grudge is behind it, and the Ramseys were a symbol of what Boulder had become.