新概念3第5课有个句子不太明白
Notonlyhadthepoormanbeenarrested,buthehadbeensenttoprisonaswell.However,hehadatlastbeenallowedtosendafaxinwhichheinformedtheeditorthathehadbeenarrestedwhilecountingthe1,084stepsleadingtothefifteen-footwallwhichsurroundedthepresident'spalace.
为什么这里用inwhich啊想不通