Name one of the mass killings where cops stopped the carnage before too many people were killed
You cant ! That's why they were mass killings and in Florida the cop stood outside which I will freely admit was a very rare situation but it still happened !
Name one mass killing where a law abiding citizen had a concealed handgun permit
You can't as they couldn't at Va Tech and far more including the woman doctor at the Texas Lubys café who saw her older parents shot and killed in cold blood along with 21 more people. She had a concealed handgun permit and could not bring her handgun into the café leaving it secured in her car because of liberal Democrat mentality creating a "Gun Free Zone of Death" . Texas later changed the law with then Texas Gov. George W. Bush signing it.
Strong evidence that liberal gun free zones KILL
https://townhall.com/tipsheet/katiepavlich/2014/09/09/the-lubys-cafeteria-massacre-a-stark-reminder-to-restaurants-telling-customers-no-guns-n1889052