has been responsible vs was responsible

I think it depends upon the context.If we are on the spot of the accident we say who is responsible for the accident.?

If we met the person after some time or we were talking about the accident later we say who was responsible for the accident?

I have searched on the internet for the usage of responsible It is used in the simple present, past and future but not in the perfect tenses when we refer to a single incident such as accident

Who has been responsible for the accident is not possible since it is a single accident

In your quote, the term responsible refers to the action leading to the accident.

responsible adjective 2 Being the primary cause of something and so able to be blamed or credited for it. ‘Gooch was responsible for 198 of his side's 542 runs’ - Lexico

While the consequences continue, and perhaps the moral responsibility as well, the action itself happened at a point in time that has passed.

The has been variant isn’t appropriate because it suggests an extended period of responsibility rather than a single episode. It can be used where the construction doesn’t allow the simple past tense, though:

• *He has been responsible for the accident. (This invites the retort “So, when did he relinquish that responsibility?”)

• The judge considered him to have been responsible for the accident. (Note 1: “to was ...” would be ungrammatical. Note 2: link to a google result that motivated this example.)