“Case” in Chinese is 案件 (ànjiàn).
警察会调查这起案件。
The police will look into the case.
Example sentence from Tatoeba (CC BY 2.0).
Not to be confused with: 按键 (ànjiàn, button or key (on a device)) · 安检 (ānjiǎn, security check (abbr. for 安全檢查|安全检查[an1 quan2 jian3 cha2]))