French police have identified a young man responsible for up to 80 robberies in student housing in the central city of Lyon through the ear prints he left behind while checking for residents.

The 26-year-old Georgian was caught red-handed in February, a police source said Friday, adding that subsequent investigations showed his ear prints on the front doors of the scene of some 80 similar robberies in Lyon.

Ear prints, like fingerprints, are unique. The man left the incriminating traces while listening in on doors to check if there was anyone inside, the official said, adding that it was an “old technique” which could be very useful.

Police said robberies at private homes had spiked in the Lyon area recently, averaging about 19 a day, often by gangs of Eastern Europeans. Lyon police arrested four Georgians on April 16 for 75 robberies.