Darko Janjevic of DW reports German authorities launched a probe into a string of deaths at a metal fittings company after an employee was caught trying to poison a co-worker’s lunch. Police found quicksilver, lead and cadmium in the man’s home.

The man was arrested for the incident in the town of Schloß Holte-Stukenbrock, northwest Germany. However, police now suspect he may be responsible for up to 21 deaths of people working for the same company.

The police detained the 56-year-old suspect in May this year, after one of his co-workers noticed an unknown white powder on his food. The would-be victim alerted his superiors and asked them to review the recordings made by security cameras, which then showed the suspect adding the substance to the co-worker’s lunch.

“In the beginning we thought it was a misconceived prank between co-workers, and not a murder attempt,” said Tilo Blechinger, the manager for the metal fittings manufacturer ARI Armaturen, to the DPA news agency.

The case escalated to an attempted murder after authorities identified the powder as lead acetate, a highly toxic and nearly tasteless substance that could cause serious organ damage.