Hasegawa has a life-or-death encounter with assassins, and the Shinsengumi and Mimawarigumi compete over solving a fictional case.
That's why you overlooked 
a vital piece of evidence.
.لهذا السّبب أغفلت دليلاً أساسيًّا
Por eso no viste una prueba esencial.
Por isso deixou passar uma
evidência crucial.