I have an artscroll siddur which gives a short explanation of each word of vidui, but then I saw a pamphlet on the vidui that the ou put out, and they say different things for the different words. So now I’m curious whether there is a book that explains vidui and quotes mekoros.
For concise explanations, you may find the following sources helpful. The Chayya Adam, Klal 143 Hilchot Yom Kippur, gives an explanation for Ashamnu, Bogadnu, etc. The Gr"a (Vilna Gaon) in his commentary on the Siddur has a commentary on the long Vidui. You can also find commentary on the long Vidui in "Michtav Le'liyahu" (Vol. II pg. 94-95) of Rav Eliyahu Dessler zt"l. For further extensive explanations with many references see Netiv Binah, of Rav Yissachar Yakobson zt"l (Vol. 5. pgs. 296-315). Chag Same'ach