Muslim working in law enforcement in a non-Islamic country

If a Muslim is able, through such work, to fight evil and oppression, or to
prevent or reduce it by using the existing laws which may contain
something of justice and decency, then it is permissible if his intention is
to seek the pleasure of Allah. He may do this work even if it involves
preventing only some people – but not all – from getting drunk, for
example.

But if it involves enforcing laws that are unjust to people – whether they
are Muslim or not – or enforcing something that goes against the
Sharee’ah, like preventing people from wearing hijaab or praying, or
giving some kind of protection to criminals, and so on, then this is not
permitted at all.

The wise and clever Muslim knows from experience to what extent his
work is in accordance with the Sharee’ah that is based on the common
good and on preventing corruption. And Allaah knows best.