The car was always there but the ladies in front are blocking most of it.
The first image below is from the above photo gallery and you can see some of the car next to the lady with the folded arms and you can see the roof a little bit to her right.
I believe the car to our left is directly in front of this car and as can be seen the perspective angle relatively shortens the length and when approximately sized, fits well within the block of obscuring ladies.

Royell's Car on the extreme left and a car directly behind, shows that the car in the above image was behind Royell's car.

In this Couch frame, the end of the car is a good match compared to the folded arm lady and the roof section as compared to the ladies in Wiegman is a similar height.

JohnM
If you look closely at the 2nd image from the top, you will see that the back seat (L) passenger door window of this "getaway" car has been obscured. From the outside, you can Not see into the car/back seat area of this "Getaway" Car through that (L) back seat window.
Immediately following the shooting, a 6th Floor shooter would have walked down the stairwell to the 1st floor, walked through the "wide open" Huge Gates, walked across the Elm St Extension, and then immediately climbed into this "getaway" car parked alongside the Island. The obscured (L) passenger window of this car, would have prevented law enforcement or anyone else from seeing a possible shooter seated in the back seat. Obscuring the view into that car, may be indicative of the shooter having a skin color that would have attracted attention at a glance.