From: ep. 3.2
Event (culprit): The wedding photographer is the (attempted) murderer.
Reference: Well this isn’t from the original canon (though the name of the murderer [Jonathan Small] and the act of Sherlock catching him by handcuffing him to luggage is indeed from the original namesake of this episode, The Sign of Four). However, this particular plot point was so uncannily like an episode from an earlier TV series, one very Sherlockian in nature, that I can’t help but think Mofftiss were inspired by it and lifted it.
In episode 1.4 of stellar TV series Lie to Me, the reason Cal Lightman, micro-expression expert, can’t see malicious intent on any of the wedding guests in the wedding videos after the groom has been shot, is that the would-be murderer is actually behind the camera. The plot there involves a jilted jealous past love, whereas in Sherlock 3.2 it involves revenge against Major Sholto (another character name from the canon original).