Herbert William Mullin was an American serial killer born on April 18, 1947 who operated in Santa Cruz, CA. 
Mullin was serving life in prison for 13 murders which he says he committed to prevent further natural disasters.  Mullin died of natural causes on August 18, 2022.
 
8 1/2" x 14" two page handwritten letter hand dated March 7, 2002 and hand signed, H.W.Mullin at the top and hand signed again at the close, Herb Mullin.

Mullin has hand signed the back, Herb Mullin. 
 
Includes the prison stamped envelope completely written by Mullin and hand signed, H.W. Mullin.
A total of FOUR signatures!