I'll bet it wasn't an AK-47 "assault rifle". I'll bet it only looked like one.
...and ammunition that can penetrate bullet-proof vests
In other words, center-fire rifle ammunition.
Here's a tip for the author: Only Class III and Class IV body armors are rated to stop center-fire rifle rounds.
Is that right? I didn't think any kind of body armor could stop a center-fire rifle round. Perhaps a lower powered cartridge but even so I have punched holes in 3/8 inch steel plate with soft point 7.62 X 39.