They have agents to investigate cases, and government agencies (FBI, ICE, DHS) are going in big for hollow point ammunition. This would be part of a larger government policy.
I guess the two questions to ask would be: 1) Is buying hollow points something new or a continuation of existing procurement policy? And 2) Why is ammunition that was long banned in wars between nations deemed acceptable for domestic use?
Hollow points are designed to expand on contact and thus, not over penetrate.
A Full Metal Jacket(FMJ) round, like the ones that the military uses, goes right thru someone. You can read accounts of soldiers shooting haj multiple times with seemingly no damage. The Green Tip round that is issued to the military is for armor penetration and is so fast that it goes thru people. Of course the wound cavity is devastating as the speed of the round does damage, but as I said, its more likely to go thru without expanding.
Hollow points are the standard round issued to pretty much every law enforcement agency in the United States.