Man suspected of killing 21 co-workers by poisoning their food: Authorities The man was allegedly seen on video trying to poison a colleague, police said.

German police are reviewing the suspicious deaths of 21 engineering workers -- dating back nearly two decades -- after one of their co-workers was allegedly caught on camera trying to poison a colleague’s lunch.

The authorities launched an investigation after finding quicksilver, lead and cadmium at the 56-year-old suspect’s home following the alleged attempted poisoning at the metal fitting firm in the small northwestern town of Schloss Holte-Stukenbrock.

The 26-year-old colleague, whom authorities have not named, noticed a suspicious, unknown white powder on his sandwich and reported it to his manager, Achim Ridder, a spokesman for the Bielefeld Police, told ABC News.

The company then installed a CCTV camera in the lunch break room. On two more occasions, the footage allegedly showed the 56-year-old suspect opening his colleague's lunch box and sprinkling something on the sandwiches during lunch breaks, police said.

After seeing the video with the alleged poisoning, the company contacted police.

The suspect, named only as Klaus O, was arrested on May 16, after police searched his apartment and found toxic chemicals such as mercury, quicksilver, lead and cadmium, Ridder said.

“Two days later, we got tests back from our criminal police laboratory in Dusseldorf, which showed it was lead acetate, a poison that could have caused severe organ damage,” Ridder said.

Tilo Blechinger, manager of the metal fittings firm, ARI Armaturen, initially believed the alleged sprinkling of a substance on the co-worker's food was a joke.

“In the beginning, we thought it was a misconceived prank between co-workers, and not a murder attempt,” Blechinger told DPA, a German news agency.

He described the suspect, who he said worked for the company for 38 years, as “conspicuously inconspicuous.”

Authorities widened their investigation after the alleged poisoning attempt of the co-worker. That probe uncovered a total of 21 cases, dating back to 2000, of employees at the same company who had died under suspicious circumstances.

Those workers died mostly of heart attacks or cancer, conditions that could have been caused by heavy metal poisoning, authorities said.

Investigators will question relatives of those workers who died and the doctors who treated them.

“We hope to have [the] first results in several weeks, as some family members and several doctors are on holidays now,” Ridder said. “And some of their bodies might have to be exhumed and examined for traces of poison.”

Separately, an ARI Armaturen employee is in a coma while another is on permanent dialysis, according to a police spokesman. Authorities suspect they may have been poisoned, too.

“Klaus O remained silent about the allegations and his alleged motive is still unclear,” Ridder said. “And he is not a chemist.”