The motive for why she committed that crime is still not well understood.
Literal
She [subject-が] why that crime [to-に] reached [question-か][quotative-という] motive [about-については], still well not-understood.
犯罪に及ぶ 'to commit a crime' — 及ぶ literally 'to reach, to extend to.' 動機 'motive.' いまだに 'still, to this day.' よくわかりません 'is not well understood.' A news-report or crime-analysis style sentence.