3 sentences

1. 这起离奇的失踪案至今仍是一桩悬案。

   zhè qǐ lí​qí de shī​zōng'àn zhì​jīn réng shì yī zhuāng xuán'àn.

   This bizarre disappearance case remains an unsolved mystery.

   Source: Dong Chinese Dictionary

2. 经过警方的深入调查，这宗悬案的真相终于水落石出了。

   jīng​guò jǐng​fāng de shēn​rù diào​chá, zhè zōng xuán'àn de zhēn​xiàng zhōng​yú shuǐ​luò​shí​chū le.

   After an in-depth police investigation, the truth of this cold case has finally come to light.

   Source: Dong Chinese Dictionary

3. 关于他离职的真正原因，至今仍是个悬案。

   guān​yú tā lí​zhí de zhēn​zhèng yuán​yīn, zhì​jīn réng shì gè xuán'àn.

   The real reason for his resignation remains a mystery.

   Source: Dong Chinese Dictionary