In The Day of the Jackal (1973), French officials abducted Victor Wolenski and torture him about who is behind the assassination mission of the French President.
He never reveals it clearly. But somehow they guess it that he is saying Jackie or Jackal.
There is no way to guess the name because he always shouts AAAAAAAAAA.. that's it. There is no word sounding near to J while investigating him.
So how did they get his name?