Three Pages

Six months after his old neighbour’s death, Sotiris walked into the police station on his own and confessed that he had pushed him down the stairs. Nobody pressured him and nobody promised him anything; he signed three pages full of detail. At the trial, while they were being read out, the policeman who had written the first report raised his hand. Why did Sotiris confess to something he had not done, and what two things did the policeman know that Sotiris did not?