Myself, I never question people (it just doesn't give good results). But if you're intent on it, you can't question other cops or your family members. Try questioning someone like a friend or a stranger. Strangers won't exactly give you the best results, however. Myself, I prefer sticking to having my Sims dig in the trash cans, just as long as they can go home to a warm shower. Rich people tend to throw out diamonds, so it's profitable as well~.