[Myrddin]

It has not been established that the shooter was wearing body armor. I researched all the news stories I could find around the time of the shooting. I found no confirmation of that speculation. It's pretty easy to deliver a full magazine of 9mm into a target before the target hits the floor. Body armor will stop most handgun calibers (9mm, 40 S&W, 45Auto) due to the large cross sectional area of the bullet. The .22 caliber .223 (AR-15) or 5.7x28 have a smaller cross sectional area and sufficient velocity to penetrate body armor. A knife will slice with body armor with ease.

[marktwain]

“It has not been established that the shooter was wearing body armor.”

I don’t believe that he was. I found at least one source that said that he was wearing a sleeved shirt with pockets for magazines, as I recall.

[Uri’el-2012]

The .22 caliber .223 (AR-15) or 5.7x28 have a smaller cross sectional area and sufficient velocity to penetrate body armor. A knife will slice with body armor with ease.

or a .357 Sig