Reply #15: Small-caliber rifles have been replacing patrol shotguns for a long time.

[benEzra]

They don't recoil as much, offer a lot less chance of ricochet and injury to bystanders, and (unlike typical police shotguns) are not useless at range. The consensus that small-caliber carbines are both safer and more suited for police use than .729 caliber shotguns was already well developed by the late '90s. For example, see Roberts G.K., "Law Enforcement General Purpose Shoulder Fired Weapons: the Wounding Effects of 5.56mm/.223 Carbines Compared with 12 ga. Shotguns and Pistol Caliber Weapons Using 10% Ordnance Gelatin as a Tissue Simulant, Police Marksman, Jul/Aug 1998, pp. 38-45.

INTRODUCTION

Until recently, the 12 gauge shotgun has remained the universally accepted shoulder fired weapon for United States law enforcement use, despite the shotgun's limitations as a general purpose weapon--short effective range, imprecise accuracy, downrange hazard to bystanders, small ammunition capacity, slow reloading, and harsh recoil. While 12 gauge shotguns still have a valid law enforcement role, especially to deliver specialized munitions and possibly in close quarters combat (CQB), recent recognition of the shotgun's significant limitations as a general purpose weapon have prompted many American law enforcement agencies to begin adopting the more versatile semi-automatic carbine for general purpose use.(12) Semi-automatic carbines offer more accuracy, less recoil, greater effective range, faster reloading, and a larger ammunition capacity than the traditional shotgun.

...

Less well known is that 5.56mm/.223 rifle ammunition is also ideally suited for law enforcement general purpose use in semi-automatic carbines.(5,6). It offers superb accuracy coupled with low recoil, and is far more effective at incapacitating violent aggressors than the pistol cartridges utilized in submachineguns and some semi-automatic carbines.

...

CONCLUSION

A 5.56mm/.223 semi-automatic carbine with a minimum of a 14.5" to 16.5" barrel may be the most effective and versatile weapon for use in law enforcement. When used with effective ammunition, the 5.56mm/.223 carbine simultaneously offers both greater effective range and less potential downrange hazard to bystanders than a 12 ga. shotgun, handgun, pistol caliber carbine, or SMG , as well as far greater potential to incapacitate a violent criminal than any handgun, pistol caliber carbine, or SMG.

...

The routine issuing of 5.56mm/.223 semi-automatic carbines for general purpose use to all law enforcement officers would significantly enhance officer safety, increase police effectiveness, and decrease dangers to innocent bystanders in all situations requiring the use of firearms.

I'm not sure if the gun the officer had was a civilian, non-automatic AR-15 or a military/police restricted automatic weapon, though. If he was on the SWAT team, he may have had the restricted automatic version.