I never responded back when they asked me why I did this
Why did you never respond?
I will get in trouble if I did respond to the request and I did steal something from the store.
It is hard to admit when we do something wrong but it is not good to ignore somebody in order not to tell them. It will not make the situation go away and they will keep asking.
Why did they have to ask me in the first place.
The store was willing to hear your side about the circumstances on why you did it. They might just forget about the whole thing if you wrote them back.