IMO, I have seen ME's get things wrong on quite a few cases. Just recently, there was the Lotto winning guy that died day after winning the LOTTO, and was ruled natural causes until family started questioning. Whoops, he died of cyanide poisoning. Its things like this where I don't necessarily agree with their opinions on things. The ME should have suspected there could be foul play right from the get-go because someone ending up dead the day after LOTTO winning is way too suspicious. So, if ME can get something so obvious wrong, what other mistakes could be made. Quite a few IMO.
The ME may have it right in this case, but for me, I think the jury is still out on whether gun was used first or last. I'm kinda leaning towards first, and someone brought up a possibility of gun jamming. If it was .25 semi-automatic, then that possibility exists the gun could have jammed after first shot with gun. I have seen semi-auto handguns jam on quite a few occasions, and if there is a jamming problem, then it could easily jam after 1 shot.
Sometimes, if the right type of shell is not bought with enough "powder" in the shell, it could cause jamming even though the right shell was bought. For instance, I once had a .380 semi-auto where I had to buy certain shells with a hgher powder grain (magnum) type shell. If I bought the lower powder (regular) shells for it, it would jam every time.
The reason the first shell works is because you manually work the action to load the 1st shell manually. As the first round fires, it ejects the casing and tries to auto-load the next shell, which is where the jamming would occur.
Semi-auto guns can jam at any point in the shooting process, but I have found when they do jam, it is typically after the 1st shell fires.
I always use "magnum" powder (larger number of grains of powder) in my semi-auto guns for this reason, and I have much less jamming issues. Also, to avoid jamming altogether, one could buy a revolver instead. To me, it is a much simpler handgun to use for new persons who want to pursue protection and are somewhat afraid of guns and their complexity.