It started with a teacup.
In 1993, a 62-year-old German churchwarden called Liselotte Schlenger put a batch of lemon cakes into the oven.
Before she had time to taste them, she was murdered.
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A neighbour who dropped around for a cup of tea found Schlenger’s body. She had been strangled with a piece of wire that had been used to tie a bouquet of flowers in her living room.
On the rim of a teacup in Schlenger’s kitchen, police found traces of DNA. The DNA belonged to a woman, but wasn’t a match for anyone in the police database.
"The only clue was the DNA," prosecutor Günter Horn told The Guardian.
Police put the case aside, hoping that one day, the woman would be arrested for another crime and could be charged with Schlenger’s murder.
In 2001, it appeared that the killer had struck again.
A 61-year-old antiques dealer, Joseph Walzenbach, was found strangled in his shop. A small amount of cash had been taken.
The same woman’s DNA was found on Walzenbach’s body, on antiques in his shop, and even on the "closed" sign that the killer had flipped around on the shop’s door.
"After 2001 we had two murders – not enough to classify the perpetrator as a serial killer but with similarities: small amounts of cash stolen, the same modus operandi in the way the victims died, both killings committed indoors with no signs of a break-in," prosecutor Juergen Brauer told The Sydney Morning Herald.
"This in itself suggests the killer builds up a non-threatening rapport before being let in."
Over the next few years, the woman’s DNA turned up at other crime scenes around Europe.
It was on a partly eaten biscuit in a burgled caravan in Germany.
It was on a toy gun used to hold up a dry cleaner in France. It was on tracksuit pants and a hooded cardigan found dumped after a string of shed break-ins in Austria.
Because the DNA was also found on a discarded syringe containing traces of heroin, it was assumed that the woman was a drug user, committing crimes to feed her habit.