Interested in Mathematical Statistics... where to start from?
When looking for texts to learn advanced topics, I start with a web search for relevant grad courses and textbooks, or background tech/math books like those from Dover.

To wit, Theoretical Statistics by Keener looks relevant:
http://www.springer.com/statistics/statistical+theory+and+methods/book/978-0-387-93838-7

And this:
"Looking for a good Mathematical Statistics self-study book (I'm a physics student and my class &amp; current book are useless to me)"
http://www.reddit.com/r/statistics/comments/1n6o19/looking_for_a_good_mathematical_statistics/