A private investigator has been unable to find the only eyewitness to the sudden death of media innovator and conservative activist Andrew Breitbart. The apparent disappearance of Christopher Lasseter, who says he saw Breitbart drop to the sidewalk in front of a restaurant, adds to the mystery surrounding Breitbart’s March 1 death. On the day the Los Angeles County coroner released Breitbart’s autopsy report, a photographic technician at the corner’s office died suddenly of suspicious causes. In addition, at the Conservative Political Action Conference in Washington, D.C., just three weeks before Breitbart’s death – where he promised to unveil “damning”...