An idea came to mind but it might be little hard to script. Basically what if every time a gun is aimed at a player or certain criminal commands like /frisk are used there would be a chance of cops receiving an alert of the general location where the crime is being done. The chance could be based off the place(map zone) where the robbery is being perpetrated i.e highway 90 % chance, urban area in desert a 40 %, middle of desert or mountain, 2 % and so on. If you want to rely on scripts then you have to consider all options since Los Santos would never be inhabited by mere 200 people at a time, so make the 3.999800 million people are scripted eyes. And the idea that if there's no AI then there's no-one to witnesses is what makes crimes so damn easy to do.