Just to add on the single shot point, I think this a bit unclear as an indicator. Generally where special forces or experienced paramilitaries have conducted an assassination, the MO involves multiple shots - for the obvious reason that it makes the intended result more likely (people surviving single head shots happens). And that's obviously easier with the automatic or semi-automatic weapons that those attackers would typically use. On the other hand a single shot is obviously lower profile.But those are all post hoc rationalisations which go from the fact that he got away for a significant period to the conclusion that it must have been professional. If you look at it element-by-element it doesn't stack up. Noone would have sat in an ops room and planned to do it at a house she rarely and randomly visited, and with easy views to the street; in broad daylight; involving physical touching; with a substandard unique weapon and ammunition; in distinctive clothing; and with a muddled and slow pedestrian exit (as per witnesses). None of these choices could realistically have been arrived at by considered planning, and comparison of options.
In other ways, single shots are more typical of untrained or inexperienced shooters - either because they don't have access to automatic weapons, are unable to perform the reloading properly on the spot, or are unaware of the chances of non-lethal outcomes with a single shot.