Musar for Menachot 109:5

לא תאפה חמץ . The prohibition to bake the part of the מנחה set aside for consumption by the priests as leavened dough which is derived from 6,9 is rooted in the above mentioned principle of אין קטיגור נעשה סניגור, that the advocate for the prosecution cannot also act as counsel for the defense. The offering which symbolized the sin must be totally burned without it being allowed an opportunity to develop mildew, etc., which could be the case while the dough rises before being baked. Hence the Torah insists that all of the dough be baked only as Matzah i.e. unleavened bread or cake. Traditionally we equate Chametz with the accuser. Thus far Rabbi Menachem Habavli.