die Kommissarin
detective
A female police officer in a leading role, especially in criminal investigation.
Die Kommissarin leitet die Ermittlungen im neuen Mordfall.
The detective is leading the investigation in the new murder case.

commissioner / detective
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detective
A female police officer in a leading role, especially in criminal investigation.
Die Kommissarin leitet die Ermittlungen im neuen Mordfall.
The detective is leading the investigation in the new murder case.

The ending '-in' is used in German to form the feminine form of many professions and roles. 'Die Kommissarin' (the female commissioner/detective) is the feminine form of 'der Kommissar' (the male commissioner/detective).
Sie ist die erste Kommissarin in der Geschichte dieser Polizeiwache.
She is the first female detective in the history of this police station.
You can tell from context whether a policewoman or a politician is meant. Words like 'Polizei' (police), 'Ermittlung' (investigation), or 'Mordfall' (murder case) point to the police detective, while 'EU', 'Kommission' (commission), or 'Politik' (politics) point to the politician.
Die Kommissarin befragte die Zeugen des Unfalls.
The detective questioned the witnesses to the accident.
In a police context, 'Kommissarin' (detective) is often combined with verbs such as 'ermitteln' (to investigate), 'einen Fall lösen' (to solve a case), 'einen Täter festnehmen' (to arrest a perpetrator), or 'Zeugen verhören' (to interrogate witnesses).
Die Kommissarin leitet die Ermittlungen in einem komplizierten Fall.
The detective is leading the investigation in a complicated case.
In a political context, e.g. in the EU, a 'Kommissarin' (commissioner) is 'für ein Ressort zuständig' (responsible for a department), 'stellt Richtlinien vor' (presents guidelines), or 'vertritt die Kommission' (represents the Commission).
Die EU-Kommissarin ist für den Bereich Umwelt zuständig.
The EU Commissioner is responsible for the area of the environment.
commissioner / inspector
'der Kommissar' and 'die Kommissarin' basically refer to the same function, but they differ in the gender of the person. In the police, a 'Kommissar' is a male senior criminal police officer, while a 'Kommissarin' is a woman in this role. This distinction also exists for official posts, for example in the EU. Learners may confuse the words because the task can be the same. The important point is: for a man, you say 'der Kommissar'; for a woman, you say 'die Kommissarin'.

Die Kommissarin hat den Fall nach drei Wochen gelöst.
The detective solved the case after three weeks.
Der Kommissar erklärt der Presse, wie die Ermittlungen weitergehen.
The detective inspector explains to the press how the investigation will proceed.