Just my thoughts:
The white car could have been making a "delivery". While sitting near the residence of the buyer (NOT anyone at 1122 King Rd) waiting for them to come outside the car's headlights were shining on some part of 1122 King and grounds (likely the side/back area).
This:
1) Caused the killer to exit 1122 King earlier than planned ( the house, or rather household, was the target), and the killer may or may not have been seen exiting the residence by the white car occupant(s).
2) The killer only intended to kill the 4 (students were the target), and while exiting 1122 may have been seen by the occupant(s) of the white car.
3) The killer may have been in the process of entering the residence when the white car pulled up and may have been seen, OR the killer might have been in the back watching the residence and been seen.
Kaylee may have let the dog out (to do his business) through the 2nd floor/ground floor slider, went up to the 3rd floor to be with Maddie while the slider was still open, and she fell asleep before going back down to call the dog in and close the slider. The dog could have re-entered the house at any time. In this scenario the slider was open and the 2nd and 3rd floor lights were on.
JMO, I think the killer had been watching the house and occupants for quite a while from behind the house. I think they live within the original request for information area (still included in the press releases). I think they traveled to/from the house on foot. And I don't think they had to walk very far at all.
Regarding the fact that the victims all had their fatal wound in their chest (as reported by the Coroner): The killer may have been targeting their hearts. IF what SG said about Kaylee's wounds is true (that they don't match Maddie's), it may have been more difficult to get the murder weapon between ribs on Kaylee's chest in the correct location due to her full bust. And Kaylee may have awoken and been moving also making chest targeting even more difficult. The liver has a Left lobe. It doesn't seem unusual that a lung would be pierced.
MOO