Thanks for your question.

I've searched a number of academic, legal, and newspaper sources to try and uncover some information on this topic. I unfortunately have not been able to locate any material pointing to CIA/police involvement in the death of Bob Sheldon.

One idea would be to contact Jon Elliston, the author of the following article: http://www.indyweek.com/indyweek/bob-sheldons-legacy/Content?oid=1183160 He might be able to provide you with some of the sources he used to write this article. Additionally, since the Internationalist is still open it could possibly help you to contact the store and see if they have any leads: http://www.internationalistbooks.org/