persons unknown meaning in English

神机暗算

Though not literally . that was done by person or persons unknown
这幕后究竟是怎样的黑手我们无从知晓
No peace , damn them ! he grumbled , with inward rage at some persons unknown
“不得安宁，该死的东西！ ”他愤怒地不知对谁埋怨了几句。
In a number of complaint cases , the complainants received an account statement or demand note issued by a mobile service operator , or a debt collection agency addressed to persons unknown to them
在多宗投诉个案中，投诉人收到流动电话服务供应商寄来的户口帐单或缴费单，或是收数公司的收数通知单，但收件人是他们全不认识的。