Your posting leaves me with more questions than answers. Most importantly, how did you come across this information regarding their method of euthanization? If this was not publically known, then you need to report it to the attorney general's office. If you specifically inquired about the method of euthanization and were not properly informed then you may have a claim. I would consult a local attorney.
This is not to be construed as legal advice. I do not have an attorney client relationship with you.