I noted those same things about the shooting. A VERY experienced shooter? Almost all handgun training is exclusively two handed grip with the dominant hand. As you get more advanced then do you get into shooting with the opposite hand, one handed shooting, how to load and shoot with one hand, etc. My training when shooting at an potential assailant inside two paces called for a two handed grip with my elbows locked to my sides for at least the first two shots. My initial reaction was this shooter was NOT an experienced shooter. But there is also the argument that while they might be an experienced shooter in the high stress moment they just simply reacted. IOW, while they might be an experienced shooter at targets they are NOT experienced at killing. At that distance though, even the most inexperienced shooter could hit the target so experience is tough to figure.
The lack of recoil while shooting one handed led me to believe this likely was not a medium caliber revolver such as a .38 Special, .357 Magnum or .327 Magnum or larger. I'm thinking .22, .22 Magnum or .32 caliber. .32's are not common, but not difficult to find. The Rossi .32 comes to mind but it isn't made any longer. Like from daddy's closet? I'm leaning toward a .22 Magnum loaded with hollowpoints. There are plenty of .22 and .22 Magnums available from companies like Ruger, Smith & Wesson, Rock Island and Charter Arms. S&W made a snubnose .22 mag in double action only that used to be common as a back-up piece for LE. Just about every experienced shooter I know that shoots a 9mm, .40 cal, .45 ACP, etc., also owns a .22 handgun of some type. Another point I consider in argument of a .22 is that Elizabeth was shot 4 times, the 4th at point blank range in what appears to be a head wound and yet even with the head wound she was still alive at the scene and survived the trip to the ER. She was still alive on life support the next day in the hospital. It's not common but there are cases of persons surviving head wounds from a .22. Make no mistake .22's are still deadly. President Reagan was shot with a .22 and even though it was only a single shot ricochet off the car door he almost bled to death before they could get him to surgery.
But while I've done a LOT of shooting on my own, in self defense training and in the military I am not certified instructor or an ER doctor, so this is strictly from my own shooting experience and personal opinion.