2 sentences

1. 逮捕他无济于事。

   dài​bǔ tā wú​jì​yú​shì.

   Arresting him is useless.

   Source: OpenSubtitles

2. 现在后悔已经无济于事了。

   xiàn​zài hòu​huǐ yǐ​jīng wú​jì​yú​shì le.

   Regretting it now is of no use.

   Source: Dong Chinese Dictionary