Paula Cassidy was an NCIS Special Agent who was originally assigned to Guantanamo Bay as an interrogator.
After that, she became the NCIS Agent Aboard on the U.S.S. Kennedy.
Following NCIS Special Agent Caitlin Todd's murder in May 2005, Cassidy was temporarily assigned to the main NCIS Major Case Response Team and was later reassigned to the Pentagon where she worked as an agent, leading her own team up until her death in the line of duty which occurred in April 2007.
Not much is known about Cassidy's history but according to her file, she was born in an unnamed area of Canada and she later emigrated to the United States, presumably gaining citizenship.
She also attended Georgetown University and while she was attending the college, serial killer, Kyle Boone was on the loose and according to Cassidy, for two years, every women in the Georgetown area was afraid to go out at night.
When Gibbs finally arrested Boone, Cassidy was relieved, owning Gibbs for the first full night of sleep she got while she was at college.
Upon graduating, Cassidy later presumably joined NCIS and was later transferred to Guantanamo Bay or "Gitmo" where she began working as an interrogator.
NCIS Season 1
Cassidy made her debut appearance in the NCIS Season 1 episode, Minimum Security (episode) where she first met NCIS agents Leroy Jethro Gibbs, Anthony DiNozzo Junior and Caitlin Todd who had arrived to investigate the death of Navy Petty Officer Khalil Sa'id.
NCIS Season 2
Prior to "Heart Break", Cassy was reassigned to the U.S.S. Kennedy, becoming its Agent Afloat.