In the previous episode, we showed how homicide detectives solved 50-year-old cold cases.

They analyzed old evidence using new DNA extraction technology pioneered by Othram, a forensic genealogy lab in Texas.

Othram provided new leads by finding relatives of suspects on genealogy databases.

As revolutionary as that seems, it was just a few years ago that the FBI pioneered the use of mitochondrial DNA in a Texas murder case.

Mitochondrial DNA is handed down from mother to child, so it can only tell you about your maternal ancestors.

In a landmark case, former U.S. prosecutor Bill Johnston used the mitochondrial DNA from a single hair to send a killer to prison for the rest of his life.

Here’s the backstory of how he did it.