has been responsible vs was responsible

Solution 1:

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.)