Kerrigan's brother, Mark, is already facing assault charges in Daniel Kerrigan's death Jan. 24, after what authorities say was a struggle with Mark. The district attorney has said an investigation is continuing on whether new charges could be brought against Mark Kerrigan.
Middlesex District Attorney Gerry Leone said Tuesday that an autopsy determined the cause of death for Daniel Kerrigan was "cardiac dysrhythmia" - a loss or interruption of a normal heartbeat that can lead to cardiac arrest - after a physical altercation with neck compression that damaged Kerrigan's windpipe. The findings also noted that the elder Kerrigan had high blood pressure and clogged heart arteries.
Kerrigan's family has disputed those findings, saying Daniel Kerrigan had a pre-existing heart condition.
Nancy Kerrigan released the letter vowing to fight, one day before she is scheduled to begin work as a commentator on the Winter Olympics for "Entertainment Tonight" and "The Insider," as she did during the 2006 games.
MORE ON CRIMESIDER
February 9, 2010 - Nancy Kerrigan's Father Daniel Kerrigan Was Murdered, Say Prosecutors After Autopsy Results
January 26, 2010 - Tonya Harding to Nancy Kerrigan: You Have My "Deepest Sympathy"
January 25, 2010 - Nancy Kerrigan's Family Defends Mark Kerrigan in Father's Death
January 25, 2010 - Mark Kerrigan: I Didn't Attack My Dad Daniel Kerrigan
January 25, 2010 - Nancy Kerrigan Family Tragedy: Daniel Kerrigan Sued Son Mark Kerrigan for $100K
January 25, 2010 - Nancy Kerrigan's Brother Mark Kerrigan Charged in Connection with Father's Death