"Guess What" Riddle

Feng is the general manager of a company. He recently discovered that his wife was unfaithful, so he hired a private detective to investigate. After obtaining evidence of his wife's affair, Feng asked a lawyer to draft a divorce agreement and a lawsuit complaint that would deprive his wife of her share of property, intending to divorce her. When Feng's wife got the news, she felt she should take action before the lawsuit. So, she immediately conspired with her lover, hired a killer to kill Feng, and staged it as a suicide so that Feng's property would be inherited by his wife. They also prepared a fake will. Feng's wife stole blank letterhead with Feng's handwriting on it, and they had the killer print the will in his office typewriter after killing Feng, leaving most of the property to his wife. On the day of the incident, the killer shot Feng with a silencer and then placed the gun in his right hand to create the appearance of suicide. Then, wearing rubber gloves, the killer typed a will that Feng's wife had dictated to him and left the scene without leaving any trace. Soon after, the news of Feng's suicide spread. Because the will had Feng's signature, everyone believed he had committed suicide. Only Feng's private lawyer was suspicious and immediately reported to the police. The police surveyed the scene and determined that Feng had been murdered. Feng's wife and the killer carefully recalled the details but still could not figure out the flaw. Question: What flaw did the police find??? It's quite simple; the flaw can be seen in the text.