Poland will formally seek Sweden's help in investigating the theft of the "Arbeit Macht Frei" sign from the Auschwitz memorial, confirming that Polish authorities suspect a Swedish link in the crime.

Boguslawa Marcinkowska, a spokeswoman for Krakow prosecutors, says her office will send a formal request for help Wednesday to the Swedish Justice Ministry in Stockholm.

Polish media have been reporting that the theft was commissioned by a collector living in Sweden, but investigators have not confirmed that.