The day when Jack Ruby shot Oswald was the day that most of America automatically thought there was a conspiracy. That is the one thing that fueled that thought - just a mere short hours after Kennedy was shot.
Strangely, Ruby’s shooting of Oswald actually argues against conspiracy. Oswald was scheduled to be transferred through the PD garage at a particular time. He suddenly decided to change his shirt, which delayed his departure by 10 minutes. That unscheduled delay gave Ruby the opportunity to shoot him. Had Oswald been transferred as scheduled, Ruby would not even have been there in time to pop him.