Who is or who was?

English as a Second Language English Vocabulary, Grammar and Idioms
1

When something goes wrong, the first thing people ask is “Who is responsible for this” or “Who was responsible for this” or what else?

Thanks.

2

Who’s responsible?
Who’s fault is/was this?
Who is/was to blame (for this)?
Who messed up? (That’s the polite version)

3

So “Whose fault is this” and “Whose fault was this” are the same thing? What is the difference between the past tense and the present tense used here?

Thanks.

4

They are not the same thing, They are different tenses.
In one, the fault is current; in the other the fault is past.