sentences:  In January 1662, a German sergeant named Hans Jurgen Radis defected to give Koxinga critical advice on how to capture the fortress from a redoubt whose strategic importance had gone hitherto unnoticed by the Chinese forces.Koxinga followed his advice and the Dutch redoubt fell within a day.This claim of a defector appears in a "post hoc" account of the siege written by Frederick Coyett, whom scholars have noted sought to absolve the author of responsibility for the defeat.