LOL - hey, some shows these days have actual ex-FBI profilers writing episodes and plot lines for them, even drawing on info from actual cases they've worked, so there's a lot of factual information tucked into those.. (is my excuse for being an unapologetic Criminal Minds junkie anyhow).
I really don't know what standard police practises are here, that way, much to my own shame. I would imagine they'd have paid attention to who was rubbernecking close to the scene. DJK was all the way across the street, afaik, so he might not have been so obvious. Or maybe he -was- noticed, and then noticed again later, and so on...
I think, just in my half-informed opinion, lol - that DJK or anyone else who's killed somebody in a frenzy of stabbing would likely not take the risk in hovering around the scene of a murder just a matter of hours later and with a heavy police presence, unless it gave them a serious thrill of some sort.
That, to me, says there was some sort of compulsion happening, that he got something satisfying out of viewing the results of his crime or needed to feel close to it. The safer thing to do would be to lay low and destroy all evidence ASAP, so self-preservation seems to have taken a back seat to whatever desire prompted that action...
Extremely loose speculation: maybe wanting to be famous or infamous was part of his motive? Wouldn't be the first.
