I do not know if you have any access to the evidence. In an affidavit by Supt. Kock, a possible blood smear on the curtain is mentioned. The photos I have of it is not very clear, but it apears to be on the OUTSIDE of the curtain. One of the two photos was clearly taken from the balcony side. My guess is that it was on the lining of the curtain, so it is possible that someone closed the curtain with a bloodied hand. It is mentioned that a sample of the possible smear was taken for analysis. Will see if I can find the results of the test.
It would be very difficult to close the curtains, close the safety gate (it is a folding type door with two sections that join in the middle) and then close the balcony door from the outside. You would then have to climb over the balcony wall and jump (it is quite high) into a garden below as there is not much to hold on for climbing other than an aluminium gutter pipe. From the garden you can leave via a gate that opens towards the road (with the fence) that we previously discussed or climb over the garden wall.
All of the above would have to happen on the side of the building that is much more visible than the front door side and there is a good chance of being seen from the parking area even if it was dark (car lights and building lighting). We do not know if the balcony door and safety gate was locked.
In summary, I think it is highly unlikely that someone would have chosen that route, but not impossible. After 16:00 the parking area side would be a bad choice to leave in such a visible and strange way, as many residents / students would be returning home and would be passing through the parking area.
On some of the photos, one can see that the balcony door was dusted for fingerprints, but no specific reference is made to it in the material we have at the moment.
Looking at it now, it is ironic that the incident took place in a flat that is so secure. Even today it is by far the best protected in the whole complex.