This is the exact definition of ex post facto law.

追溯法令就是这个意思。

In my opinion-- and as such, it is a ex post facto law.

依我所见 法律不能追溯之前的行为。

So anxious is a young conscience to discover a palliative, that the ex post facto nature of a reason is of no account in excluding it.

一颗年轻的良心如此急切地想找到一种缓和剂，以至于一个原因的事后性质在排除它方面没有任何意义。

What he was about to say, he told me, was an " ex post facto rationalisation" — a deduction, from the vantage of the present, of what he might have been thinking at the time of the murders.

他告诉我，他要说的是“事后合理化”——从现在的有利条件出发，推断他在谋杀案发生时可能在想什么。