In the interest of being especially nitpicky and hoping someone can offer an explanation that doesn't make the mystery seem quite so contrived, why does the photographer stalk the soldier, constantly taking photos of him? I'm assuming he already had the idea of what to do (hence targeting him as a trial run) so what does he have to gain from spending days taking photos of him other than raising suspicion? Also I thought it was weird that the woman with the "ghost boyfriend" used John's middle name when introducing him, it's something that literally no one would ever do.
Taking photos and stalking the soldier was to "practice" or "test" his method of murder.
The bit about the woman mentioning John's middle name involves seeing the invitation at the Mayfly Man's place.