Xavier pointed out a piece on 'Cop Attackers &

Their Weapons', well worth reading. Couple of excerpts:
Among other things, the data reveal that most would-be cop killers:

• show signs of being armed that officers miss;
• have more experience using deadly force in “street combat” than their intended victims;
• practice with firearms more often and shoot more accurately;
• have no hesitation whatsoever about pulling the trigger. "If you hesitate," one told the study’s researchers, "you’re dead. You have the instinct or you don’t. If you don’t, you’re in trouble on the street..."...

...
Several of the offenders began regularly to carry weapons when they were 9 to 12 years old, although the average age was 17 when they first started packing "most of the time." Gang members especially started young.

Nearly 40% of the offenders had some type of formal firearms training, primarily from the military. More than 80% "regularly practiced with handguns, averaging 23 practice sessions a year," the study reports, usually in informal settings like trash dumps, rural woods, back yards and "street corners in known drug-trafficking areas."

One spoke of being motivated to improve his gun skills by his belief that officers "go to the range two, three times a week [and] practice arms so they can hit anything."

In reality, victim officers in the study averaged just 14 hours of sidearm training and 2.5 qualifications per year. Only 6 of the 50 officers reported practicing regularly with handguns apart from what their department required, and that was mostly in competitive shooting. Overall, the offenders practiced more often than the officers they assaulted, and this "may have helped increase [their] marksmanship skills," the study says.
And, as if it weren't known already,
Predominately handguns were used in the assaults on officers and all but one were obtained illegally, usually in street transactions or in thefts. In contrast to media myth, none of the firearms in the study was obtained from gun shows. What was available "was the overriding factor in weapon choice," the report says. Only 1 offender hand-picked a particular gun "because he felt it would do the most damage to a human being."

Researcher Davis, in a presentation and discussion for the International Assn. of Chiefs of Police, noted that none of the attackers interviewed was "hindered by any law--federal, state or local--that has ever been established to prevent gun ownership. They just laughed at gun laws."

Thanks to Xavier for pointing to this.