Death by a single letter

Dr Thon Hughes is a virologist who receives a letter, full of loathing from an anonymous person. In only about five minutes or so, he dies a mysterious death. Sadie, his wife, does not hesitate anymore and calls help right away. She takes a picture of the letter and rushes to the police department where she is introduced to a former detective — G, Sebastian Rober, and Elbert Macaulay. Sadie is anxious to find out who the murderer and urges the team of three. By urging them, she has drawn herself to the spotlight and the rest suspects her openly. Aghast, Sadie realizes her un-natural behaviour and settles down. The investigation continues and more clues and ideas open up when she shows them the photograph of the letter. Elbert leaves the room shortly, reporting he had paperwork to do. Now, G and Sebastian listen to Sadie's story and G comes up with a conclusion when a thought strikes him. Now the suspect shifts to Elbert Macaulay, who had said the same words when he had taken the interview. G decides to do a confrontation, a very unusual choice that he rarely chose. They barge into Elbert's office, keeping him at gunpoint and G gets a phone call. Leaving the gun in Sebastian's hands, G answers the call and returns to them with a pair of handcuffs to use it on Elbert. Apparently, G had found the evidence of Elbert's fingerprint traces on the gloves he had used when he passed the letter to Thon. Elbert accepts his doing and says that he was doing it for a good cause, but Sadie is not ready to accept anything from a criminal. Days pass, having to visit the magistrate a few times and one day, she comes across a metal crate, belonging to Thon. She opens it and her worst nightmares had become true. Sadie realizes that Elbert had been true from the first, except his methods. But, it's too late for her to consider it because...