I noticed murky images of clothed men reflected in mirrors inside gloomy bedrooms where nude women sit on iron bedsteads. I saw impending violence and death. I saw a victim who had no reason to fear the charming, handsome man who had just coaxed her into a place and state of utter vulnerability. I saw a diabolically creative mind, and I saw evil.

I began adding layer after layer of circumstantial evidence to the physical evidence discovered by modern forensic science and expert minds.

All along, forensic scientists and I have hoped for DNA. But it would be a year and more than a hundred tests later before we would begin to see the first shadows of the 75- to 114-year-old genetic evidence that Walter Sickert and Jack the Ripper left when they touched and licked postage stamps and envelope flaps. Cells from the inside of their mouths sloughed off into their saliva and were sealed in adhesive until DNA scientists apprehended the genetic markers with tweezers, sterile water, and cotton swabs.

The best result came from a Ripper letter that yielded a single-donor mitochondrial DNA sequence, specific enough to eliminate 99% of the population as the person who licked and touched the adhesive backing of that stamp. This same DNA sequence profile turned up as a component of another Ripper letter, and two Walter Sickert letters.

Genetic locations from this DNA sequence were found on other Sickert items, such as coveralls he wore when he painted. The DNA in all but the single-donor Ripper stamp is mixed with other genetic sequence profiles from other people. (This is neither surprising nor damning.) The DNA evidence is the oldest ever tested in a criminal case.

This is only the beginning. We aren't finished with our DNA testing and other types of forensic analyses. These could go on for years as the technology advances at an exponential rate.