March 2019
You need a metro police level 8
You make your police sims work shifts and collect the necessary resources
1250 Flashlight, 320 Handcuffs and 225 Fingerprints
You can trade resources, top left (police badge), 3rd tab (the one with two arrows) when you're in the station, to get more of what you need
I have two grunts (in addition to the two specialized police), not specialized, to collect resources, so I can usually finish a shift in 4 hrs.
As soon as the specialized police have earned their badges and leveled up enough, I'll send in the grunts to get resources
It takes a lot of shifts and trades to get enough for the K-9 and Forensic lab - even more for the upstairs rooms, but it can be done without LPs
Even if you don't get walk-ins with the right resources, you should still do them all to get the police coins so you can trade for more space and the things you need