Should one person be used for this purpose? The issue of paradoxes was brought up. In the end, they decided to go ahead with the project.

To limit influences from the past, the only information given was that a note and a piece of skin were needed to be placed in the gun.

Once they reached a stage when they thought the assassin was ready, the began the final phase. One of the scientist took a piece of paper. He didn’t know what to write, so he wrote DNA Sample on it. The assassin was sent him back in time

The assassin knew it was now time to act. He had his finger on the trigger. Once he pulled the trigger, the circle would be completed. For his whole life he was told that this is what he has to do, nothing else

Once the trigger was pulled, his life would be free. Free to make his own choices. The target was in sight. His destiny awaited. His finger started to pull the trigger, then it stopped for a second. He was tired of being told what to do. His finger did not pull the trigger.The circle was broken.