When Krystal stabs Jack Davis (her former boyfriend) in the back, he falls to the floor after leaving a blood stain on the shower door. When Krystal kicks him in the stomach to prevent him from reaching for the phone, you see his back, but with "NO STAB WOUND".
When Sandra, with Nathan's help, is trying to get into Preston's social media account and she eventually manages it, his profile page is already displayed on the screen as she is making the final keystroke.
When Nathan discovers Jack Davis's body, he calls 911 to report the stabbing, but does not give the location (or his name), so the emergency services would not know where to go.