Here is a VERY in-depth article about Johnny Lee Wick's (the gunman) background. It's a very telling tale of a lifelong violent criminal who finally decided to go out in a "blaze of glory"...
http://www.lvrj.com/news/Authorities-81-shots-fired-at-courthouse-shooter-80727872.html?numComments=43
This article states that Wick's used a Mossberg shotgun, and fired a total of 5 rounds, killing one security officer and wounding a Deputy US Marshall in the arm.
LEO's returned fire (including the first victim, who, reports say, bravely got one shot off before he was slain). This report says that LEO's fired a total of 81 rounds at Wicks--the final shot that put him down was a head shot. It has been reported (but not confirmed) that Wicks was hit TWICE--once in the stomach and once in the head:
Wicks: 2/5 = 0.4 = 40%
LEO's 2/81 = 0.025 = 2.5%
So I guess I was wrong. The responding officers in this incident had a hit ratio that was less than 10% of the national average for LEO gunfights.
Looks like some re-training is in order in Las Vegas...