John seems like the obvious choice, given that he was furious with Clare for deceiving him into believing that she was white throughout their entire time together. After discovering the truth, he sets out to confront her at the party that she and Irene are at. John is fuming as he demands to see Clare and storms inside the home. "You liar!" he shouts out at Clare, who's standing near the window Irene opened earlier. He then calls her a "dirty liar" and runs towards Clare who falls out of the window, though it's unclear if he actually pushes her or not.
Visibly shaken up, John runs out of the apartment and he's later seen sitting in the snow near Clare's dead body. When the cops question Irene about what happened, one of the policemen says that Dr. Redfield told them that John shoved Clare, but Irene tells him that she's "quite sure she just fell before anyone could stop her."