David Berkowitz aka The Son Of Sam .44 caliber serial killer. 

Original angry typed letter numbered #006, dated September 14.
He has written below the close, "Stop reading this letter you bastard!"

Includes the original prison issued envelope postmarked September 17, 1979.
Hand signed, "David Berkowitz 78-A-1976."

David Berkowitz 1979 Letter and Signed Envelope Set