A camouflage-clad German man wielding a samurai sword attacked at least seven hikers in forests west of Berlin, performing sword tricks before ordering them to leave the woods.
Police suspect a 46-year-old local man who trained in martial arts and survival skills in camps in Papua New Guinea and Vietnam to be the attacker.
"He's dangerous and has been hard to find because he wears camouflage," said Catrin Feistauer, spokeswoman for the Nauen police department.
Police have used infrared cameras mounted on helicopters to try and track him down.
The man pushed two elderly people off their bikes and flashing his sword shouted at them to leave the forest.
He later tried to drive a young couple out of the woods.
No one was seriously hurt.