What happened to the fourth knife?
It's strongly suggested during the trial by Naz's initial lead attorney Chandra Kapoor and in the closing arguments by replacement lead attorney John Stone that the knife was likely taken by Duane Reade if the brute of few words indeed committed the crime, but we here at home know that Duane Reade didn't kill Andrea, thanks to Detective Box's strong detective work post-retirement.
So where's the knife? Well, we seem to be left with two possibilities: Ray Halle used it to kill Andrea and later disposed of it (after confronting Ray at the Atlantic City casino, Box shows the prosecutor photos from security-camera footage hinting that Ray may have dumped some trash from his car on the night of), something that will probably be a hot topic during his impending murder trial. But I've also thought: isn't it possible that the fourth knife from the set in Andrea's kitchen had been missing for years? Knives can break, can't they? They can be disposed of -- intentionally or accidentally -- in other ways not involving murder, right? Like, I'm pretty sure that my dishwasher has swallowed 13 of my steak knives whole over the years and not even a rejuvenated Detective Box would be able to find them.