Warning! Spoilers for Run below.
In director Aneesh Chaganty's Diane (Sarah Paulson) crept up behind him and stuck him with a tranquilizer. Tom was never seen again in the movie, but his ultimate fate was left relatively unknown.
Run tells the story of Diane caring for her ill and wheelchair-bound daughter, Chloe. Once Chloe's mother attempts to slip her a new pill, she starts to become suspicious. As the movie goes on, Chloe becomes downright terrified of Diane, and eventually manages to escape the house in order to search for help. She comes across her friendly local mailman Tom, who immediately believes her story and wants to help her escape.
Unfortunately for Tom, Diane tracks down Chloe and catches up to them. After Diane injected him with a tranquilizer, his fate was all but sealed. A brief shot later confirms that things did not end well for Tom the mailman, showing the lengths that Diane was willing to go to in order to protect her secret.
The first act of Run sees Chloe investigating a mysterious pill that her mom is trying to off as a new medication. Once Chloe learns that it's a pill intended for dogs and a person taking it could make their legs go numb, she realizes she needs to leave immediately. She crosses paths with Tom, who offers to help. But when Diane catches up to them, it's all over for Tom. After revealing to the camera that she has a gun in her possession, she sticks him with a tranquilizer. In a blink-and-you'll-miss-it moment in the following scene, Diane is shown dragging a body through the hallway of her home. The body seems to be wearing sturdy boots on its feet — just like those a mailman would probably wear.
This all but confirms that Diane killed Tom off-screen. She believed she needed to go to such lengths to protect a secret she'd been harboring for far too long. Munchausen Syndrome by proxy, so she pumped Chloe full of drugs to keep her sickly, ensuring her daughter would always need her. Diane made sure they lived a solitary lifestyle so no one would discover them. So when she came across Tom attempting to help Chloe, Diane knew he would blow her cover. So in her head, killing Tom was the only way to protect it. Chloe resented Diane once she learned the truth, proving that Tom's murder was never necessary.
