Just imagine the situation when a possible crime accomplice has to prove his alibi.

试想一下，当一个可能的犯共犯需要证明自己不在犯时的情形。

When Filch wasn't guarding the scene of the crime, he was skulking red-eyed through the corridors, lunging out at unsuspecting students and trying to put them in detention for things like " breathing loudly" and " looking happy."

费尔奇如果不在犯巡逻，便瞪着两只红通通的眼，偷偷隐蔽在走廊里，然后突然无防备的学生，千方百计找借口关他们禁闭，比如说他们“喘气声太大”，或“嘻皮笑脸”。

Whether there is proof that the defendant was not on the crime spot is essential in proof of his innocence.

证明被告不在犯的证据对证明他的清白非常必要。

You can offer no defence, no alibi — only a mere assertion which would not deceive a babe! — that you are not guilty.

你不能提供任何辩护， 也不能提供不在犯的证据——只是一个不会欺骗婴儿的断言！——你是无的。