Their motives remain a mystery.

他们的动机仍然是个谜。

《牛津词典》

Worst of all, the identity of the attacker may remain a mystery.

最糟糕的是，攻击者的身份仍是一个迷。

youdao

The immediate fallout of the king’s declaration has never been documented comprehensively; important aspects remain a mystery.

国王的政策带来的直接影响从没有详细可靠的文献记录；关键部分仍旧是个谜团。

youdao

They prefer that it remain a mystery, much like Edgar Allan Poe himself.

VOA: special.2009.02.02

The exact circumstances of 19-year-old Johana Casas' murder, in July 2010, remain a mystery.

BBC: Latin America & Caribbean

The motive for such a horrific act is likely to remain a mystery to us all.

CNN: Details, but no answers, in Oregon mall shooting

Their views remain a mystery, nor do their papers' opinions give a steer.

ECONOMIST: Tory leadership