I always understood, based on the gemarra in Yoma 9b, that the Jews were guilty of the three cardinal sins during the First Temple period (murder, illicit relations, and idol worship). However, I recently saw the Ben Ish Chai, in his commentary to Eichah 1:1, that the Jews were guilty of transgressing the Ten Commandments.
והנה בבית ראשון עברו על עשרת הדיברות, ולכן נפגמו שתי ההי"ן, שהם רומזים לעשרת הדיברות שהיו חמש מכאן וחמש מכאן
I was wondering if he's the first to say this, or if any earlier source says this idea? A quick search on Bar Ilan bore nothing.