Most people that kill themselves do so on a whim. Its probably not the case, but its not impossible. I'm guessing either the coroner is corrupt, or they have actual evidence it was a suicide. If it was a murder, then I doubt Boeing would do it without assurance it couldn't be traced back to them. So regardless of what actually happened, the only official story there will ever be is that it was a suicide. That is, unless Boeing is as reckless about murder as they are about building planes.