Helen's suspicion of her husband's involvement came from putting together observations: son has been showing fatigue and lapses in physical coordination; husband steps in to relieve her of the task of taking son to doctor & later gives dismissive, benign (and false) account of the diagnosis; doc who was perfectly…

The doc's death was only suspicious to his wife at first, and that could easily have been attributed to the denial stage of grief. At that point, only the viewers and John know that it was murder. Also, Helen KNEW that Thomas had visited the doctor. What she picked up on was John's reaction to Alice's suspicion and…