The 39-year-old woman, named only as Kirsten S., was running through the forest at around 8:50 am on Saturday when she was attacked by the young man who stabbed her five times before leaving her for dead.
She was still alive when a passer-by found her and she was able to describe her attacker before she passed out and died.
The man is said to be between 15 and 20, around 1.75 metres tall and slim with fairly short, dark blond hair. He was wearing a white top and long, white trousers, and was riding a bright red bicycle.
Thomas Scherhant, head of the murder task force in charge of the case said his detectives were still mystified by the case. “We are investigating in all directions,” he told the Berliner Morgenpost, adding that they were not ruling anything out at this point.
He also suggested that Kirsten S., who worked as a psychologist for cancer patients at Berlin's Charité hospital, may have known her attacker.
“Perhaps she came across him without knowing it. A considerable amount of physical force is necessary to kill someone with a stab to the upper body. Someone stabbing five times is the sign of a great hatred.”
He suggested it was not the kind of killing where the victim was randomly chosen.
Detectives have sealed off a large part of the woodland to search it for evidence, and are appealing for locals to report any sightings of the suspect.