I made a lookup in the copyrights base (http://www.copyright.gov/records/cohm.html) and the rights are divided between Arkham, Donald Sidney-Fryer, Richard E. Kuhn and Steve Behrends. Those claimants have copyrigths to various colections and compilations of CAS material.

I find this a bit confusing since im been toying about the idea of translating CAS stories and try to get them published comercially. Who owns the rights to the stories themselves? Who should be contacted for rights to other (non-english)language versions of the stories?

Sincerely
ArveK

CAS' literary executor is William A. Dorman, CAS' stepson, now professor emeritus of journalism at California State University in Sacramento. Contact me offline and describe your project and I'll put you in contact with him.
Best,
Scott