Japanese police have arrested a factory worker for allegedly poisoning frozen food with pesticides, in a case that sickened more than 2,800 people across the nation, news reports say.

Gunma Police Department arrested the 49-year-old man, identified as Toshiki Abe, who works at a frozen food factory in Gunma, north of Tokyo, run by a subsidiary of Maruha Nichiro Holdings, Japan’s largest seafood firm, according to public broadcaster NHK and other local media.

The suspect denied the allegations, while the motive behind the alleged crime was still unknown, NHK reported.

Local police officials declined to comment.

The subsidiary, Aqlifoods, received the first of a series of complaints in November, with a customer saying its frozen pizza smelled like machine oil.

But the firm did not announce a product recall until December 29, after tests found traces of a chemical called malathion, which is used as a pesticide and to treat head lice.