“Follow the money.”
—Money-laundering detection instructor
Any investigator who has ever solved what was once considered an unsolvable case knows the feeling of accomplishment that normally stems only from painstaking work (and sometimes a little luck). Many cases are solved because of the investigator's planning and organizational skills, case knowledge, identification of witnesses (and getting them to voluntarily cooperate), interviewing skills, the collection of evidence, and the timely utilization of appropriate investigative techniques, tools and resources, and so on.
During my professional career, I've received training from experts in the field in formal and informal settings as well as through my own studies. However, there's no substitute for experience. Some of the best investigative skills (especially interviewing skills) usually are progressively developed in the field. And those skills often are developed by learning what not to do. It is just as important to learn from your mistakes as your successes. And it's even smarter to learn from other investigators' successes and mistakes!
NOTE: I prefer to use the words “mistakes” or “shortcomings” rather than “failures” because I don't believe in failure. As long as you learn when things don't work out, those are just lessons learned. Most lessons learned usually provide greater dividends down the road. When training young patrol officers and investigators, in addition to teaching ...