Wouldn't it make sense in such a case for the salesperson to have a way to contact the authorities to inform them about suspicious cases?
Considering they already do background checks in most states, there is simply nothing a person can do to stop a previously law-abiding citizen from killing people with legal firearms. Complete and total prohibition would stop many, yes, but not all, compounded with the problem of illegally owned guns, which are in the vast majority, of which such legislation would have no effect.
but isn't it a little suspicious when one person buys so many weapons/explosive merchandise
Well, unless you propose you jail me for what I'm planning to buy for my 18th birthday, I'd go for "it really doesn't matter."
Of the amount of weapons legally purchased, even in quantity (not uncommon for people who might run gun clubs, etc.), very few will end up being used in crime by the original purchaser. That's not to say they won't be stolen and used in crime, as this is a very common problem, but taking something away from law abiding citizens because it might be obtained via theft by criminals is quite frankly absurd.
But massacres do show one thing: there is not enough control about the actual sales
No amount of background checks, insanity checks, waiting periods, or prohibitions will stop somebody from killing others if he wants to, especially in America. These people come in, are completely normal, and act like regular customers, and rarely buy weapons in bulk over one counter. If they want to kill people, they don't even need to buy the weapons, as you can pick any random house in America and it will probably contain a firearm.
So, prohibit weapon/ammo sales via internet? Oh wait, that would make it impossible to buy any sword via internet too. How about just ammos then? *exhibits hypocritic smile*
This isn't as practical, or good, of an idea as you think. Some calibers (.338, .416, .50, 5.7x28, .243, .500/.470/.375 nitro, etc.) you simply aren't likely to find at any random gun store. While some may have a dozen rounds, or a package of 20, if one was aiming for a long day at the range for some R&R shooting targets at long distances, then chances are they're going to be cut short by running out of ammo if their uncommon ammo type simply isn't available at their local gun store.
Not to mention more popular rounds, .223, 9mm, 12 gauge, etc., are available at gun stores by the tens of thousands and it isn't uncommon for somebody to come in and purchase a box of 440 or 880 at a time, sometimes multiple boxes. You would be surprised just how little ammo 1000 rounds really is.
what happened to the shooter is he in jail for life??????
He'll likely get life. In Texas they'd slap him with the needle and fast track him there, but alas, he's not here.