My opinion is that if SWISS have investigated the case and decided that in their view they are not liable under 261/2004 they would be only too happy to share their evidence with you.

If that evidence is sound you would understand their position and see that pursuing your case would be futile.

The fact that they claim to have evidence which exonerates them but choose to withold it from you only gives rise to doubts about the veracity of that evidence.