THE FOURTH MONKEY, by J. D. Barker
The story switches between the present day and the creepy, horrible diary entries. At first one feels some compassion for the young writer in his bizarre situation, then as the entire story unfolds it becomes clear that motives and actions aren't as they had seemed. Porter, reading the entries while trying to figure out not only the killer's motivation but why the killer made his fatal stumble, realizes he has only hours to figure it out before another death may happen. Too late, Porter realizes that the web he has followed is as much a trap as a trail.
A 4 for me. The diary entries were a bit too pat. But the story, particularly the very tense and dramatic denouement, was worth reading.