Killing the boss

It was the evening before the Christmas Eve in one usual company. The secretary was  feeding the cattle in her computer game. Other clerks tried to finish their work as fast as possible, dreaming to come back home to their families & have a nice dinner. But accidently the staff heard the scream from the headman`s office. The secretary found the boss lying on the floor with knife in his back, his shirt & the floor were in blood. Max, the most strong worker in such things, called the police & a doctor for a secretary. Everyone was shocked & frightened with that event. But since time the majority of workers realized that the killer must be one of them. But who could do such a terrible thing? Well, the police investigation had to help in such situation. But not everything was so simple as seemed to be. The investigation didn`t find any pieces of evidence or fingerprints on the place of murder. So, the identity of killer wasn`t determined so fast. All the workers were in tension all the next week. They were trying to guess who could hate the headman so much to to kill him before the Christmas. But during the process of searching the killer, the workers realized that all of them were in good relations with their boss & with group at all. So, this case had a dead end. "What could happen there?" this question flooded all the thoughts of the curious secretary. So, next morning she decided to look at the place of the murder onr more time. And she was very surprised finding the headman working at his computer. He was glad to see her & told her all the truth, that he had planned that "mureder" for long time just to examine his group, was each of members deserve to work with him.