The biographer has been given unfettered [ʌnˈfɛtərd] access to the family's collection of personal correspondence.

unfettered [ʌnˈfɛtərd]
adj

Unfettered describes what is not controlled or restricted. It is a synonym of both free and unrestrained.

A fetter is a chain or shackle for the feet (such as the kind sometimes used on a prisoner), or, more broadly, anything that confines or restrains.

Fetter and unfetter both function as verbs in English with contrasting literal meanings having to do with the putting on of and freeing from fetters;

English