Lew, the cops were probably busy "establishing a perimeter," which means cowering behind their vehicles (including tanks), as they did at Virginia Tech a few years ago, at Johns Hopkins hospital last summer when a doctor was shot there, and elsewhere. They usually get all dressed up in military-style garb for the TV news cameras and hang out acting all macho until the shooter either kills himself or is apprehended by civilians.
In the recent Arizona murders, the two men who apprehended the shooter were not unarmed. They were both on network news this morning, and one of them said,"I carry a firearm, so I wasn't really afraid" (to tackle the shooter and hold him until the police finally showed up). He probably saved quite a few lives by doing this, and may not have had the nerve to do it had he not been carrying a firearm.