Watch How I Met Your Murderer Full Movie Free Online 123Movies. Mack Meyer has built a large fanbase discussing true crime on her wildly successful podcast "How I Met Your Murderer." However she finds herself the center of the story after learning her husband, Henry, was involved in the death of his high school sweetheart, Lily. With the help of her new neighbor, Oliver, Mack links Lily's death to other murders in the area and fears she may be living with a serial killer.