Why did the killer ride past the victim a good distance, then turn around and shoot at him from the opposite side? Some possible reasons: riding further before turning around in order to observe the surroundings; shooting from the front after taking a good look at the victim's face, either to make sure it was not the wrong person (though it's likely the killer had followed the victim around previously and was familiar with his yellow bike and his appearance/posture enough not to need such confirmation) or out of extreme personal vendetta. Another possibility, if the killer was determined to shoot at the victim's head to endure fatal result (I feel sorry for such a speculation), as we see in the picture Dr. H had a hunched posture on the bike so it would be hard for the killer to target at his head from the back .