When we are faced with names of local institutions, there is always a dilemna : "to translate or not to translate"...
I always tend to think : "not translate". In literature "traduire" can be "trahir" but it is more risky and "touchy" in the field of legal language. That means leaving the word in its original language (in italic for instance) with if needed a few explanatory words
Especially in your case as the French and American legal systems are very different and work differently.
Should I have to translate an American text talking of the "Grand Jury", I would keep it as such, and would not write "Chambre d'accusation" instead
In your case, you could write for example :
"The Chambre d'Accusation", control chamber/organ/instrument prior to court judgement, decides to maintain the accusation of murder..."