Kind of fun to see all the speculation. That aside, going beyond some very basic observations is unwarranted.
You can tell the pistol is some kind of semi-auto equipped with a suppressor and that it's not cycling with the suppressor--requiring the shooter to manually work the action for each shot. He does this so fast after the first shot, without pausing to diagnose the malfunction, that I would say he expected this behavior.
The semi-auto appears to be conventional in appearance--looks like a rectangular profile slide, no obvious cutouts or unusual shapes. We can be reasonably sure it's a locked breech design of some sort based on the fact that suppressors don't affect the function of straight blowback designs and the provided information that it's a 9mm. There are a few blowback 9mms out there and some other operating systems, that would be more tolerant of suppressors, but it doesn't look like any of the blowback pistols I know of, and the other operating systems are pretty unusual/rare.
I have a problem with the idea that it's something really unusual and distinctive like the Station 6 for a couple of reasons. It looks very conventional, unlike the Station 6 and it would be very foolish to use such a distinctive and rare pistol in a crime that's likely to be witnessed and on video. The guy was pretty careful about trying to conceal his identity and seems to understand he's going to be videotaped. Pulling out a weapon that would immediately narrow the suspect search down to hundreds instead of thousands, AND that would focus the search on a group of people who had to submit a photo and fingerprints to make the purchase seems inconsistent with that effort.
Sure. All of the information, including the video and pictures of the suspect could have been altered before being released. Maybe the murder never even happened at all. You have to start with some reasonable assumptions or discussions like this are pointless. If we start from the assumption that the released information has been intentionally altered, then there's no real point of discussing this at all based on that information.
how did the shooter know when and where the victim would be precisely?
It doesn't appear that he knew "precisely". Witnesses say he waited around for hours in the general vicinity.
