Police say they have dropped an investigation into allegations by Stamford Board of Education Vice President Lorraine Olson that board Secretary Dolores Burgess had threatened to physically assault her. Bureau of Criminal Investigations Lt. Diedrich Hohn said Friday the investigation has been concluded because investigators were unable to substantiate the allegations after interviewing several witnesses. Hohn said many parts of the videotape had been muted and, if a threat had been made during one of those segments, police would not be unable to use it to obtain a warrant for a threatening arrest.