Police do not solve crimes. Police enforce laws. Detectives solve crimes. I would expect that detectives and police officers would be held to different standards.
i.e. if the maximum IQ for a beat cop is 110, naturally the maximum IQ for a detective will also be 110.
The police union is mostly responsible for this, because they don't want people coming in from outside and skipping the grind to become detectives.
Most large cities have their own police academy or there's a regional academy that several cities use. Police academy is usually three or four months of intensive training that new recruits go through (a little like boot camp for the armed forces). After graduating from an academy, the officers are sometimes rotated through probationary assignments and then given a more permanent assignment.
Detectives and other specialists are generally promoted out of the ranks of police officers.
My brother is a cop and an inspector (detective for you in the US). He's smart but not at all bookish. So he's got the right "cop" personality and the fact that he was smart was a good thing.
Now that he's hiring cops, he's careful to only hire "smart" cops if he has a sergeant position opening up in a few years or if he's ok with them moving on to a new department in 3-5 years.
My uncle was a "dumb" cop for 25 years. He was quite happy writing tickets and arresting people for the bulk of his career. He only took a sergeant's job when street work got to hard on him physically.
In the US, there is one for police: police academy and then work your way up the ranks to detective, etc.