(SNIP)
Why are there no traces of this man in the apartment, simple, he wore gloves. And secondly, because so many people (20+) were running in and out the apartment before forensic managed to seal it off, that so many traces were disturbed and lost anyway.
(SNIP)
I think there were 50 people in the apartment when police arrived- it wasn't that forensic couldn't "manage" to close it off fast enough. The scene had been hopelessly compromised before that time.