Snipped and BBM.
Nearly all handguns are semi-auto, unless they're revolvers. It's unlikely it was a revolver-- brass has to be ejected manually, and there is a lot of brass there (most revolvers hold 6, 7, or 8 rounds). The location of the casings will be close to where the shots were fired, not where the people were shot (ie, where the bullets ended up). So, from where the brass is, we know approximately where the shooter/s was/ were.
The relatively tight cluster of brass (by the markers) suggests, IMO, that the shooter/s were not moving (ie, not running) while firing those particular shots. Nearly all semi-auto handguns eject the brass on the right side, and depending on the firearm and caliber, the brass travels about 4-10 feet (unless on an incline, a smooth surface, ricocheting off another object, etc). Given that these are in a gravelly/ grassy area in an alley, that's most likely where that particular shooter/s was firing from.
Most handguns have magazines that hold 8-10 rounds. A few handguns have magazines that hold more, but they're not common (and >10 rounds mags not legal in some places). More than 20 rounds fired (more than 20 brass casings found, according to reports) suggest that either the shooter re-loaded 1 or more new magazines, or had another gun loaded and ready, or there was more than one shooter. Empty magazines can't be re-filled very quickly (probably takes 15 seconds and good dexterity to go even that fast), but having pre-loaded magazines takes less than 2 seconds to eject the spent magazine and insert a new one. Reports say the shooting went on for more than one minute. A determined shooter can easily shoot 10 rounds (full magazine) in less than 10 seconds if they want to.
The size of the holes in the home siding pics, and the distance from where the rounds were fired, suggest a larger caliber, rather than a smaller caliber round, IMO. I'm estimating 50 feet or more from the alleyway (presumably at the end of the yard) to the home, from other pic views. And given the distance in the pics of the brass markers, I can see a good sized brass casings in some pics, so I'm guessing it was larger than a 9mm. My best guess is a .357, .38, or .45. Big, powerful rounds. Sure sounds like these folks were ambushed and intentionally targeted.
