Who told us that Dorner killed this guy and the other two?
LAPD of course.
Now that doesn't mean he isn't the perp, but the source of the information is "tainted" at the minimum.
Dorner is suspected in three deaths, one in Riverside and the other two in Irvine. Riverside and Irvine have their own PDs with each conducting its own investigation. Both departments are completely independent of the LAPD. Your assertion is absurd.