FRANKFURT — German prosecutors said Thursday that they were investigating whether a Volkswagen manager encouraged employees to destroy or remove documents last year, shortly before the Environmental Protection Agency publicly accused the carmaker of illegally manipulating emissions tests in the United States.

Volkswagen employees have told investigators that a person in a supervisory position sent clear signals in August 2015 that they should remove evidence. While the person wasn’t explicit, “everyone understood,” said Klaus Ziehe, a spokesman for the state’s attorney in Braunschweig, Germany

The investigation, previously reported by several German news organizations, could raise the stakes for Volkswagen, which is already under intense scrutiny by authorities in the United States, Germany and other countries.

The E.P.A. formally accused Volkswagen of clean air violations on Sept. 18, 2015. The company has maintained in court documents that top executives of the company did not grasp the gravity of the accusations until shortly before the E.P.A. announcement.