COPENHAGEN, Denmark (AP) – Police in northern Sweden said Thursday they were looking into the unexplained deaths of three men who had died within a short period after working at an electric vehicle battery plant in the Arctic. They want to find out whether the deaths are linked, whether a crime has been committed, or if they are a string of accidental workplace fatalities.

The deaths have puzzled Swedish media which have reported about the three people who died after working at Northvolt’s plant in Skelleftea, some 620 kilometers (385 miles) north of Stockholm. Two of them died in January and February, while a third one passed away last year. Two were working at the plant and the third one was a cleaning person.

Local newspaper, Norran, said that a 33-year-old cleaner was found dead in his bed in January, the day after his evening shift. A month later, a 19-year-old employee was also found dead in his bed hours after late-night work. Last year, a man in his 60s was found dead on his balcony after having worked at the plant, the newspaper said.

Police investigator Johan Stabbfors told The Associated Press that an investigation has been opened, noting “there is some kind of indication that there has been some type of exposure in one of the cases.” He did not elaborate.

An anode oven at the Northvolt Ett AB plant in Skelleftea, Sweden, on Thursday, Feb. 17, 2022. Sweden’s Northvolt is leading an effort to forge a regional champion that can beat rivals from Asia. Photographer: Mikael Sjoberg/Bloomberg via Getty Images

Stabbfors said that police had to “be open to the fact that there can be other circumstances” responsible for the deaths.

“But for now, we have nothing,” he said of the probe that was opened last week.

Matti Kataja, head of communications at Northvolt, told Swedish broadcaster SVT that the company had done its own investigations which didn’t show any accident or exposure. Kataja, who was not immediately available for comments, welcomed the police probe.

On its website, Northvolt said its customers include several heavyweights in the automotive industry. The Stockholm-based company claims to have over 6,000 employees in Sweden, Germany, Norway, Poland, Portugal, the United States and Canada. Earlier this month, German carmaker BMW canceled a huge order with Northvolt for battery cells for its electric vehicles, due to production delays.