Answer:
They believed that Lee Harvey Oswald had been working for a conspiracy, and that a second gunman was involved. This was contrary to the Warren Commission, who had believed Oswald to be the sole perpetrator. However, even at the time this was controversial. For example, evidence for the presence of a second gunman came from a Dictobelt (a sound recording device) that was attached to a police motorbike, but an amateur researcher suggested that the recording was recorded later than the Committee had asumed.