I posted this on the FNAF wiki, but I'm chipping it in here, as this's what I've personally ascertained so far. Please be warned, massive spoilers.
[quote] In the 7th Night, or 'Custom Night', you don't play as Jeremy Fitzgerald. As [LINK:http://img2.wikia.nocookie.net/__cb20141111213018/freddy-fazbears-pizza/images/9/91/FNaF2_Pink_Slip.png[1]   ] shows, you play as Fritz Smith, who is fired on his 'First day on the job'.
I will go so far as to extend my theory into the circumstances of FNAF2 being that Jeremy Fitzgerald, the 'protagonist' of FNAF2, is responsible for the children missing (the papers on the wall of FNAF1) and the resulting investigation that Phone Guy talks about. Having access to the 'Parts/Service' room, he wore the 'Golden Freddy' costume in order to lure children away. The reason the 'Toy' or 'New' animatronics attack in the first night (your first day on the job, where the old animatronics aren't active) is because they're "tied to a criminal database". Jeremy Fitzgerald is likely using an alias, but is known by the law enforcement as a child murderer and/or paedophile. His face is recognised by the new animatronics.
From the second night onward, the 'old' animatronics boot up and begin their attack. The minigame involving 'give gifts, give life' is likely The Puppet/Marionette - for whatever reason - being able to tether the now murdered children's souls to the costumes out back - the only thing available to do so with. The old animatronics are much more aggressive than the 'Toy' ones, in that they will physically rip the Freddy Mask off if they get a good look at you before you put it on. The old costumes are now 'revenants' - the children's souls have been 'given life' in the form of the old animatronics; they are angry, and want revenge.
Back to the initial point - on the 6th Night, you're informed that there's one more event that's booked in before the pizzeria closes for the forseeable future - 'a birthday'. My hypothesis is that Jeremy turned up to work that day, and was the recipient of 'The Bite of '87' - at the hands of one of the animatronics, as they had unobstructed view of him, and he had no mask to conceal himself. After the bite, the police (who are obviously already swarming over Fazbear Entertainment) would obviously be drawn to someone being nearly decapitated - and would then get a bead on what was the night watchmen, and realise they had the fugitive child murderer on their hands.
Not once in the papers in FNAF1 did it state that the man who was suspected of causing the disappearances of the children was charged. This is likely due to him being reduced to a vegetative state by the loss of his frontal lobe - but surviving. You can't charge someone who can't speak in their defence.
This explains why you play as 'Fritz Smith' on the 7th Night. You're a new night watchman who tampers with the animatronics as soon as he gets there, and is fired on 'the first day on the job'. [/quote]
Someone chipped in about the first guy who worked the night shift who was moved to the day shift. I replied.
[quote] Yeah, he did say no new systems come out without a 'kink'. Though the previous night shift worker may well have just left due to not liking the fact the animatronics can move around at night. Anyone would be unnerved by it - but he wasn't killed, even without the Freddy Mask or a remote connection to the music box. The animatronics came looking, but didn't attack - despite him being completely defenceless. The safety measures only came into place after he left - and you; Jeremy Fitzgerald - are the first to use them. [/quote]
I'll also add here, that the Phone Guy says in Night 3 that the day guard, who /was/ the night guard, 'has reported nothing unusual'.
First post on Reddit. Go easy on me!
!!!EDIT!!! I'm adding to this. I did a little searching and found something. Jeremy Fitzgerald is the name of a real-life stuntman. In 2011, he received a wound during the filming of 'The Avengers' film. The wound scalped him, removing a portion of the front side of his head. Jackpot?
SOURCE: http://www.aceshowbiz.com/news/view/00041676.html[2]
!!!ADDITIONAL EDIT!!! Fritz Smith, or Fritz Langford-Smith, was an audio engineer who specialised in vacuum tubes, power supplies and recording equipment. Phone Guy says he'll take on the night shift after you leave - Night 7, or 'Custom Night'. Furthermore, the phone messages in FNAF1 are actually recordings - not realtime phonecalls. Finally, FNAF1, obviously, runs off a power conservation mechanic.