Well I haven't finished looking over everything, so I don't have much to back me up yet when I say I'm not the killer.
All I have now is this:
"One down… 19 to go!" leads me to believe that it was the serial killer so both murders could be done by the same person. Simply that there are 21 people playing take away the killer leaving 20, killing one more leads to 19. It's not a clue leading to me, but the fact that it was the serial killer.
But what got my attention the most was "Somewhere in the back of the house a CD was playing."
Now I may not have said much, but that doesn't mean I haven't been here looking over posts. When I read that I was immediately reminded of leaderofstars, and how he kept posting music videos and he also has music playlists in his comics. Also, compared to the other people running for mayor, he said very little which can lead towards the whole, being quiet clue.
Then I saw that martinlo_23 mentioned something about WWI planes piloted by cats, which points to the whole "there are no dogs, blah blah" clue and the WWI documentary playing during the murder. And the shadow clue, with his sonic sprites.
I'll continue searching to try to prove to you all that lynching me wouldn't be the correct way to go.
for the record i have an ipod not a cd player, and dogs love me.