A quick look at the internet confirms that it is, indeed, a common practice of most law-enforcement agencies to not hire people with significantly above average IQs, based on the theory that smarter cops will become bored and quit. Some agencies, such as the FBI, require advanced education, so they will probably have higher IQs. The increased use of educated forensics experts probably helps to increase the intelligence level of the over-all force, but I really think that other steps to help attract and retain more intellectual police would help improve police/civilian relations. Of course, we should realize that we also need officers who can relate to all people, including those who are intellectually impaired.
Those of us with higher IQs (last time I was tested, mine was 170) do need to realize that a person with an IQ of 100 is not stupid (the average for cops seems to be 104, according to several internet sites). I have known people considered intellectually impaired who were capable of thinking much like a person with a well above average IQ (creative-divergent type thinking) and I have known people who were supposed to be above-average (even having advanced degrees) but who had very rigid, un-creative intellects. IQ is not the only significant facet of intelligence.