Como dizer "Por que será que..." em inglês

Hello friends!!

I'd like to know if this sentence is right or not:

Why is it that you did it?
Por que será que você fez isso?

I'm asking this because I always remember people refering to this sentence as:
I wonder how you did it

So I'd like your help, because I'm teaching English and I sometimes have doubts about some structures!

Thanks, anyway!!