"The Perfect Murder" is a short story by the British politician and author Jeffrey Archer, first published in his 1988 anthology A Twist in the Tale.
He leaves unnoticed, then anonymously tips off the police so that the man he saw, a 51-year-old insurance broker called Paul Menzies, will be arrested.
The murder inquiry receives vast media attention and Paul Menzies is eventually arrested and brought to trial.
The protagonist is eventually sacked from his job, and puts his family life on hold, attending the courthouse hearings every day.
His guilt grows ever larger, and he is consumed by the fear that Menzies will be found innocent and the police will identify him as the real murderer.