When Vincent Tabak told friends at a dinner party soon after Joanna Yeates' death that her killer must have been a "detached, crazy" person, no one at the table thought that he, more than anyone else, knew the truth.
After all, the 33-year-old Dutchman appeared polite, considerate, hard working and highly educated. He was noted for his quiet but cheerful nature.
Yet the seemingly devoted boyfriend was in fact a fan of submission pornography in which women were choked, bound and gagged. His computers revealed images of females being held by the neck, degraded and sexually abused. He surfed sex sites for escorts, using the cover of business trips for his assignations.
He had been looking at online pornography the morning of last December 17 - the day that prosecutors said he murdered Yeates.
His double life can only be revealed now, after a jury rejected his claim that he had strangled his 25-year-old neighbour to death by mistake.