Too many police know essentially nothing about guns.
The theoretical cyclic rate of fire for a full-auto M16 ranges from 650 rounds per minute to 800 rounds per minute. That's on full auto. BUT ...
While there are 40-round magazines out there, they aren't reliable so the magazines of choice are typically 30-rounders. Even on full-auto, the maximum rate of fire is slightly more than 10 rounds per second, so a full magazine dump takes between four and five seconds. After which, the firearm is empty, and doesn't shoot until reloaded. So the actual rate of fire is severely affected by how fast the shooter can reload, and how quickly the firearm overheats.
But the "assault weapons" we see in "civilian" hands are not full-auto military firearms, they are semi-automatic rifles. The sustained rate of fire is still subject to magazine capacity, time needed to reload, and overheating considerations, and in addition to how fast the shooter can repeatedly pull the trigger.
The latest reports about the Sandy Hook shooting indicate that the shooter fired approximately 150 rounds, total. The time interval still has not been accurately pinned down, at least in any report I have read. Early estimates said three to five minutes, other reports said it took the police 20 minutes to arrive. Even if we take the very shortest time that has been yet mentioned -- three minutes -- that's only 50 rounds per minute, or 100 rounds in two minutes. That's ONE TENTH the rate suggested by the police "expert" in the opening post, and this is from the recent, actual, real world shooting that sparked all the furor.