First of all, Bob Taylor was once kidnapped by Mr. and Mrs. Jones, in the same way Alex was (and Anna and Joy for that matter). But Bob achieved to escape before getting killed (Mrs. Jones even mentions completely forgetting about him, until he appeared in the news recently). The reason why he is so deranged in general is just because of the traumatic experiences he had back then. It is hard to explain in particular what his actual insanity was, especially since I'm absolutely not an expert on the topic, but basically the kidnapping left some deep scars in his soul from which he never recovered (in the same way like Alex isn't really to call "normal" either).
In the same way he is obsessed with mazes because Mr. Jones, who once kidnapped him, was. Bob was himself presented with this strange imagery and sentences like "if you solve the maze you can leave" when under Mr. Jones' possession. And once he got this discredited book "Finding the Invisible Man", written by an FBI agent about a mysterious maze-loving kidnapper (and while it's not completely clear if the book actually was about Mr. Jones, it's definitely connected to him), into his hands, those memories all broke through and he started to recreate those kidnappings, maybe up to the point of pretending to be this maze-kidnapper himself.
As a result he worked himself further and further into the fantasy of kidnapping children himself. That is the reason he bought/stole children's clothings, smeared them with pig blood and buried those boxes full of dolls in his garden. He was immitating the "Invisible Man", pretending to have kidnapped/killed the children, even if not ever doing it for real. Maybe this even went up to the point of where he himself believed to have actually done it for real, which might be the reason he shot himself in the interrogation room (though, that might also have had other reasons, like a general discontent with his soul-torturing life).
As to the snakes, I'm not sure their connection to Mr. Jones or the "Invisible Man" was ever mentioned (but it wouldn't be too far-fetched, given the many religious motifs throughout the movie, and especially in Mr. Jones' motivation).
So to sum up, Bob Talor didn't ever participate in any kidnapping, apart from his own, where he was the vitctim of the same kidnappers that got Alex, Anna, Joy, and all the unkown others. And it was that kidnapping that put him in a deeply deranged state and ultimately drove him to play through fantasies of kidnapping and child murder, though never doing it for real. He was thus in some way a red herring/wrong track, while on the other hand still being connected to the actual kidnapper and utlimately helping Loki to figure out the whole picture.