Aとは言わないまでも and Aとは行かないまでも are usually interchangeable, and they mean ";if not A", "I don't mean A, but ..." or "I won't go so far as to say A, but (at least) ...". This までも is an old way of saying "even though", so you can think of it simply as と(まで)は言わないが. Your sentence roughly means "I'm not saying she has killed them, but (at least I would say) she's the only person you can interrogate".

The linked example is the same; it means "It's not something that can fulfill every wish, but still it's more than valuable for a magician."

By the way, many J-E and E-J dictionaries list "not to say" as a valid translation of とは言わないまでも, but according to this and online E-E dictionary definitions, it may be a mistake. For example, 暑いとは言わないまでも暖かい means "It is warm, if not hot" rather than "It is warm, or even hot".

Aとは言わないまでもB and Aとは行かないまでもB are usually interchangeable, and they mean ";B, if not A", "I don't mean A, but B" or "I won't go so far as to say A, but (at least) B". This までも is an old way of saying "even though", so you can think of it simply as と(まで)は言わないが. Your sentence roughly means "I'm not saying she has killed them, but (at least I would say) she's the only person you can interrogate".

The linked example is the same; read the answer carefully. The sentence means "It's not something that can fulfill every wish, but still it's more than valuable for a magician."

By the way, many J-E and E-J dictionaries list "not to say A" as a valid translation of Aとは言わないまでも, but according to this and online E-E dictionary definitions, it may be a mistake. (Isn't this English idiom counter-intuitive?) For example, 暑いとは言わないまでも暖かい means "It is warm, if not hot" rather than "It is warm, or even hot".