BERLIN (DPA) - A German court will deliver its verdict on Thursday (March 7) in the trial of a man accused of attempted murder for allegedly poisoning his co-workers over the years by serving them tainted sandwiches.

The accused - a 57-year-old identified as Klaus O, in line with German privacy laws - was arrested last year in the aftermath of 21 deaths of company employees in the town of Schloss Holte-Stukenbrock.

While the high number of deaths initially prompted the investigation at the company, it has still not been proven that any of the dead individuals were poisoned.

Klaus O was discovered after a co-worker found a white powder on his sandwiches. A hastily installed security camera then caught him in the act.

Footage showed him going to his colleagues' bags, taking containers out and sprinkling powder on the sandwiches before calmly re-packing everything.

Investigators found chemicals including lead acetate, cadmium, lead and mercury, as well as a notebook, at Klaus O's residence. Evidence found on his computer also indicated an interest in chemicals.

A psychologist said during the trial that Klaus O "came across like a researcher who was trying to see how different substances affected rabbits". Another psychologist said he was not mentally disturbed and should be held criminally liable.

Two of his colleagues suffered serious kidney damage, while another had brain damage and is presently in a vegetative state and has to be cared for by his parents.

The court in the western city of Bielefeld is expected to deliver its verdict at 3pm local time (10pm Singapore time). State prosecutors have recommended a sentence of life in prison, followed by preventative detention.