German police are losing hope of finding who left a box of vials with hamster DNA on a train.
The find caused alarm in the south-western town of Heidelberg last week.
Federal police sent a bomb squad to investigate after a train driver found the styrofoam box with three vials of liquid on a local train on Friday.
Forensic specialists later determined that the liquid contained genetic material from rodents.
Officers had hoped to crack the case by publicising the unusual find, but despite intense media interest the owner has remained elusive so far, said Jan Doering, a federal police spokesman.
Police had already disposed of the vials as the cold chain had been broken.
Heidelberg is home to several research centres, including the European Molecular Biology Laboratory.