My ideas:

 

Bank Robberies

scale traffic.

dead people

Way for a close examination

Observations on houses of suspected criminals

Some good ideas some not, Bank Robberies would be hard because there are no banks in GTA 4 that you can go in in (apart from in a mission)   , Scale traffic can be done using Traffic flow by Sam you can use the ini file to change how much or how little traffic you want. dead people.... thats more of a Medical Examination mod but a good idea.You can see where this is going however they are good ideas   just with lots of difficult barriers to over come. See if you could get someone like abraxas or someone else who have made mods that use this kind of thing. 

There are 2 bank robbery scripts.

 

http://www.gta4-mods.com/script/museum-and-bank-robbery-mod-v103-f2195

http://www.gta4-mods.com/script/armoured-truck-robbery-f15136