So who's heart is in the box?!?

Nicole Wallace was a recurring villain in Law and Order : Criminal intent. Though she faked her death multiple times in that show the last time she was seen her heart had been cut out and sent to the lead detective in a box by the detectives mentor. The DNA verified that is was indeed her heart. Huge fan of the character and all , and I hate to sound like Brad Pitt in the movie Se7en , but what's in the box , ahhhh....c'mon man whats in the box?!? If it wasn't her heart and the DNA results were wrong than and that sexy little Aussie number is still alive that who's heart is in the box? thanks for filling me with a question that will never be answered now seeing as Criminal Intent isn't on air anymore : P