How would violating journalistic principles help someone build a reputation?

If the name leaks, the leak can be subject to criminal liability and civil damages, hence no reputable and attackable source would publish it to general access.

Do you think more than maybe a tiny fraction of french employers would read obscure online forums, or be involved in organizations, where such a name might circulate? i find that highely improbable.

Your article shows that the problem is the "tough on crime" approach that led to deteriorating relationships between the people and the police. It further says those to be vital to be able to identify and arrest suspects of serious crime, which in turn leads to polices inability to police murder in Baltimore. That no police officer was convicted after the dead of Gray further eroded those relationships

So the article emphasises, what you seem to argue against. It is crucial for the police to be able to effectively take its role, that the police itself is properly policed and violations by police officers are met with consequences.

To get back to France, killing someone in a traffic stop certainly will not help to build relationships and trust between the community and police.