Forensic science has a few tricks up its sleeve that we would never know about unless they are used to solve some crime we are following. Cracked collected stories of crimes that were pulled off by seemingly competent criminals with little conclusive evidence, until some genius hi-tech crimefighting capability was launched. Solving these crimes took both modern technology and the investigators' imagination to use them. Look deep enough, and they can find their way around even the most clever perpetrator.
Vincent Brothers was a bad man. Not Shaft bad, but "commit mass murder on your own family and then smugly lie about it in court" bad. In July of 2003, the elementary school vice principal flew from California to Ohio to supposedly visit his brother, but in reality, the trip was his planned alibi. Once he landed in Columbus, he rented a car, drove back to Bakersfield, CA, and waited for his wife to come home with his three children and his mother-in-law. He then shot and/or stabbed all of them to death, including his six-week-old son. Once he finished staging a break-in at the house, he drove the rental car back to Ohio and enjoyed the rest of his trip like nothing happened.
So how did they convict Brothers? By bringing in entomologist Lynn Kimsey to examine the insects on the front of the rental car, which told the story of exactly where that car was driven, fortunately before it was washed. She could even tell what time of day he drove by the bugs! That's just one of seven such stories of great detective work, in a list at Cracked.