The cooling off time is ultimately exactly why we finally need regulation. Gulliani was just on CNN talking about this yesterday.
Once more with the assumption that when someone is determined to mass murder people (paraphrasing him here) "Whether its with knives or poison they'll find a way".
Total BS
All these rampages prove it comes down to ease of use.

Ya know when we did have people poisoning Tylenol in the past , we made it harder for them to accomplish it. We put in the safety features so that if your tylenol was messed with , you'd at least know. We certainly didnt make it "impossible" for someone "determined" to poison people to be able to accomplish it , but the small deterrent was enough.
The determination sort of wears off when it isnt as easy as point and click