Police have arrested a man suspected of killing as many as 21 engineering workers over two decades at a valve manufacturing company in western Germany, reports CNN. The 56-year-old metal-fittings worker, identified only as Klaus O, was caught on surveillance video sprinkling a powdery substance onto a co-worker’s sandwich in May; security footage confirmed the event after the co-worker found the white substance and alerted his bosses. "In the beginning, we thought it was a misconceived prank between co-workers and not a murder attempt," a company manager tells the DPA news agency, per Fox News. The police identified the substance as lead acetate, which is highly toxic and can be fatal if ingested. A search of the suspect’s home turned up “poison-making materials,” per Newsweek, including mercury, lead, and cadmium.
After discovering the poisonous materials, police widened their investigation to include 21 employees of the company who have died since 2000, and may exhume those bodies. Although the deaths were attributed to natural causes at the time, according to CBS, police say they included a "remarkably high number of heart attacks and cancers" and could have been caused by heavy metal poisoning. Police are also investigating the possible poisoning of three living employees. Two are in a coma (one for two years, according to the Times of London) and the other is receiving dialysis treatment. A man who worked with Klaus O for three decades fell mysteriously ill three months ago with kidney failure, and wonders if he too is a victim. “Doctors could not explain why I got so sick,” the man tells Bild, per Fox. Police have assembled a 15-member team to investigate the deaths. Klaus O has so far only been charged with attempted murder. (Read more serial killers stories.)