Early analysis suggests that a violent structural failure rather than an engine explosion may have caused the crash of Virgin Galactic LLC’s experimental rocket ship Friday, according to safety experts and one person familiar with details of the investigation. The National Transportation Safety Board’s probe of the accident is just beginning and it could change direction, these people said. But based on video footage and preliminary data analysis, they said, investigators are focusing on aerodynamic forces that could have caused the dramatic in-flight rupture of the craft, which killed one pilot and seriously injured the other. Because some engine malfunctions...