In the book, In Cold Blood, who was Willie-jay and how did Perry describe him?

Willie-Jay was the chaplain's clerk in the prison. He is described in the following way;

During the first of his three years in prison, Perry had observed Willie-Jay from a distance, with interest but with apprehension; if one wished to be thought a tough specimen, intimacy with Willie-Jay seemed unwise. He was the chaplain's clerk, a slender Irishman with prematurely gray hair and gray, melancholy eyes. His tenor voice was the glory of the prison's choir. Even Perry, though he was contemptuous of any exhibition of piety, felt "upset" when he heard Willie-Jay sing "The Lord's Prayer"; the hymn's grave language sung in so credulous a spirit moved him, made him wonder a little at the justice of his contempt.