How do you build a case map in detective career?

All good advice. Take your Sim on patrol. Remember your Sim is a Rookie. Eventually, they'll be assigned to a case with a more experienced officer. Your job will likely be to photograph and collect evidence. Sometimes you'll even get to dust for fingerprints. This is all part of training. When the Chief deems your Sim is ready, you'll get the work task to find an assignment. Then you get to take your Sim on their very own case. Once you've visited the crime scene and collected the evidence, when you bring your Sim back to the station, analyze and log the evidence, then you should be able to click on the board at the back of the computer room.