The challenge for the prosecution is that voluntary dismissal is not entirely free of legal risks and consequences. Jeopardy may not attach until a jury is seated, but still, a defendant's Constitutional rights to a speedy trial and Due Process may prohibit the prosecution from re-filing the case, especially if the reason for the prosecution's action is to gain an advantage over the defendant.
Also, dismissal is not a decision the prosecutor can make alone. The DA must file a written motion explaining the reason for the request, and it is the judge's decision whether or not to grant the motion. Rest assured that if Stanley files to dismiss without prejudice, BM's defense will be demanding dismissal with prejudice, arguing that the prosecution can't avoid judicial rulings barring admission of evidence by dismissing and re-filing.
In addition, dismissal without prejudice will not toll the statute of limitations on the non-murder charges, which IMO are important to the prosecution's strategy.
All MOO. If there are attorneys out there with a better informed view of the voluntary dismissal strategy, I would welcome their comments.