This isn't new, it was just hard to figure out. And I wanted to add it to my Baltimore Primer .
What exactly was argued in the acquittal of Officer Nero was hard to figure out. Mostly because the State's Attorney, Mosby, has repeated changed her story. Initially she claimed the stop of Freddie Gray illegal and the arrest was illegal. But that wasn't true. There was clear reasonable suspicion for the stop, and the knife is probably illegal -- or at least a reasonable officer could believe so, as said by a court commissioner -- so the arrest was legal. (And no, despite what Mosby has argued, cops don't have to ask about the legal justification for a foot pursuit to join in.)
So what the prosecution tried to argue, which is really quite absurd, is that because of the length and style of the detention -- the time when Gray was already in handcuffs (as is standard after catching a fleeing suspect), at some point during the period between the legal stop and the subsequent arrest -- at some point the stop became an arrest before the knife was found. And at the point of arrest, the legal standard needed by police would rise from "reasonable suspicion" to "probably cause." So if an arrest happened before the knife was found, police officers would not have had probable cause for an arrest. This is an amazing, novel, and almost incomprehensible legal argument. And it rightly failed in the trial of Officer Nero.
The other issue that will come into play, especially in the Goodson trial, is denied medical care. It's not clear that this happened at a criminally negligent level. But even if there was no crime, at least the basic legal argument here makes sense.