Okay, to clarify : the initial release version will only have the features that you see in the video, as well as a few extra's that will be added over the next month or so. It will take place in a small test district with five or six houses, including your own. There won't be a day and night cycle : it will always be night. The NPC's will only have simple schedules. They will either sit and watch TV, wander around their house or sleep. The cops will behave exactly as they do in the video. No jail : the game will end if you surrender to them. Each NPC's scream or struggle will create a random chance of the cops arriving. The "You hear sirens!" prompt will be removed so you won't know when they arrive. You will have a simple character creation system, where you can choose your name, appearance and basic stats. The preset characters based on real serial killers have already been removed. There will be basic weapons : blunt weapons and slashing weapons, as well as pistols and shotguns. I'll also try to make it so that you can use severed limbs as weapons.
It will get boring after awhile due to it's initial simplicity. Your enthusiasm is awesome and it will definitely go towards me adding features and tweaking the game based on your ideas, but don't think all the awesome shit being talked about will be available from the get go. There will probably be a substantial delay after the first release, with months passing before new versions are posted. I've got a wife and a full time job, and this is merely a fun little toy that I build and play around with every now and then.
In conclusion, most of the things being discussed will not be available for some time and I have not set any of the future features in stone, so some might be scrapped or changed as time passes. I'm not a professional game designer. I'm an intermediate programmer with messy coding habits and this is my first attempt at any sort of game with actual structure and purpose. I'm used to coding applications.
You mentioned the decomposition of corpses, and how this could be masked or accelerated in order to allay suspicion or just get rid of the corpse. What about preserving a corpse, turning it into a longer-lasting trophy that you can keep around to decorate the place and fulfill your psychopathic needs? The skill could also double as a profession and source of tools. And, hey, have you ever met a taxidermist who wasn't creepy?
I'm thinking that corpse decomposition should work as such :
Decomposing NPC's will have a circular radius created around them. Let's call it the zone of decay (like Miasma in DF). The zone of decay will expand outwards as time passes. Things like walls, chemicals and other things should slow or stop the radius from expanding further. If another NPC passes over a tile that has the zone of decay trigger on it, they will become suspicious. This will set off another trigger that will make the police automatically seek out the center of the zone. Then they will find the source. This concept can be applied to individual severed limbs as well.
Of course, the problem with that is that I have not decided on map creation and how to divide the map itself. I've thought about random generation and I don't want it. The replayability of the game will be in the world interactions and the large amount of distinct characters that can be created. So the ideal way to go about it is to hand craft different districts with as much detail as possible. But the problem with districts is that I'd have to simulate the one's that you aren't present in, which makes the idea I posted above a challenge to implement.