Well, he mentions the Australia law. DC was just forced to repeal its handgun ban, so it's not like restrictions haven't been attempted or even implemented with huge public support in certain areas. Australia groups guns into categories - for handguns:
To be eligible for a Category H firearm, a target shooter must serve a probationary period of 6 months using club handguns, after which they may apply for a permit. A minimum number of matches yearly to retain each category of handgun and be a paid-up member of an approved pistol club.
So in this specific case, where a guy ordered a gun just to murder people in retaliation for something recent, I'm guessing having to jump through hoops like belonging to a target club and applying after 6 months, participate in matches with other target shooters, etc - then yeah, I'd say there's a good chance that if this kind of law was in place a few years ago then by now he'd have to go to extraordinary measures to acquire something like a pistol filled with hollow points.