Sometimes it's not what you do but how well you do it. My personal experience with a case at my friends fast food police, the Royal Malaysian Police just called in the suspects, and after few hours, they managed to find all the accomplishes and the stolen customers' wallet and gold chain. There weren't any cctv just some hearsay that these were the last people seen finding the item.
If you don't have the skills, no matter how you talk or interrogate, you'd never get the results.