in mitigation

so as to make something, especially a crime, appear less serious and thus be punished more leniently

以減輕情況（尤指罪責(zé)）的嚴(yán)重程度

in mitigation she said her client had been deeply depressed.

為了減輕罪責(zé)，她說她的當(dāng)事人一直深陷抑郁之中。