(CNN) — A court in Germany has sentenced a 57-year-old man to life imprisonment for poisoning his colleagues’ sandwiches.

The man, identified under local law as Klaus O, added dangerous heavy metals to food items at the factory where he worked in the town of Schloss Holte-Stukenbrock over several years, according to CNN affiliate RTL.

The court in Bielefeld, North Rhine-Westphalia, found him guilty of attempted murder Thursday and imposed the maximum custodial sentence.

The judge said the crimes were as serious as murder, according to German news agency DPA.

Two victims have been left with serious kidney damage and a third is now in a vegetative state after falling into a coma, RTL reported.

Klaus O refused to speak during his trial and the motive for his actions is still unclear.

However, a mental health expert for the prison service told the court that the defendant wanted to see how the poison would affect his colleagues, like a scientist performing tests on a rabbit, according to RTL.

In May 2018, a security camera captured Klaus O opening a co-worker’s lunchbox and putting a substance on the sandwich inside, the police said in a statement in June last year.

A small bottle of a “powdery substance” was found in the suspect’s bag after he was taken into custody, police said.

The owner of the sandwich had raised the alarm earlier, after discovering an unknown substance smeared on his lunch. He informed his company’s management, which in turn notified police.

Testing by the regional criminal office of North Rhine-Westphalia indicated the substance on the bread was toxic lead acetate, and there was enough to cause severe organ damage, authorities said.

Authorities broadened the investigation after two other cases of illness at the company in recent years were discovered.

Klaus O was brought before a judge on May 17, who issued an arrest warrant for attempted murder.

Fire brigade specialists found mercury, lead and cadmium in the suspect’s apartment in Bielefeld. Police said the man “has long tried to produce toxic substances, including heavy metal compounds,” based on substances found in his home.

CNN’s Nadine Schmidt contributed to this report.

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