Casey was a Fenian agitator. He was tried at Cork before Judge Keogh for high treason. Mr. Casey, who was then 19 years of age, had contributed a series of inflammatory articles which the solicitor-general stated were remarkably effective in spreading the doctrines of Fenianism. Casey spent five years in penal servitude, part being spent in the prisons of Portland and Pentonville, and the remainder in West Australia where he developed a close relationship with John Boyle O'Reilly .
