I have a lot of respect for good detectives. I really enjoyed "Homicide Hunter" - which is a retired detective's recollection of past murder cases. Who knows how much was myth vs fact, but I got the sense he kept good notes because he would speak to exacting detail about decades old cases.
One of my favorite episodes was his first homicide case. A gas station was robbed and the clerk was killed. No video, no prints, etc. However there was a necklace that was dropped. It had some kind of pattern, so he called every. single. jeweler in the area. He called a lot, and eventually got a hit and found his man.
It's this kind of diligence and dedication (plus technology) that can crack cases open, even cold ones. Like the article here, he found 4 untested hairs that cracked it open.
>How did he know that it was dropped by the killer and not some random customer?
As any diligent investigator (not just of the criminal justice type) can tell you, he didn't, but it was something to dig deeper into and then hopefully find the next piece of information that it connects to. In this case that was just the identity of its buyer, but from there he could scrutinize that person to see if anything else about them lines up, or if they were just coincidentally there.
Usually, if you track someone down based on something very circumstantial, but they really were the guilty party, you'll eventually find other information to cement that connection.
It's not as if he would have found the owner of the necklace and arrested them right then.
One of my favorite episodes was his first homicide case. A gas station was robbed and the clerk was killed. No video, no prints, etc. However there was a necklace that was dropped. It had some kind of pattern, so he called every. single. jeweler in the area. He called a lot, and eventually got a hit and found his man.
It's this kind of diligence and dedication (plus technology) that can crack cases open, even cold ones. Like the article here, he found 4 untested hairs that cracked it open.