A possible explanation

Rating: 8/10 (28 December 2017)

The guy who threatened Mildred and then bragged to his friend about a similar rape had the same modus operandi as the real killer. He definitely knew the real perpetrator which is why he went to scare her off her quest, meaning he had a stake in this. Since he was in Iraq at the time of the murder, it is apparent that a fellow soldier of his did it while off rotation, as a case of not being able to stop what they got used to doing there. The guy said that the rape and setting ablaze of the victim had been his obsession ever since, so probably it was the same for the real rapist.
In the end, Jason and Mildred did not turn around, albeit being hesitant to go all the way with their plan once there. The moment Mildred would have recognized the guy from the shop, they would have realized that he definitely had some connection and would have extracted a confession out of him as to who the real killer was - most probably someone in his unit who was currently on his tour.
Personally, I think that they would have solved the case, given the circumstances as no way they were dropping all the facts as a mere coincidence. Had he not revealed who the other guy was, they would have killed him instead, since he was basically the same type.