Berlin: Authorities have opened an investigation into 21 deaths at a company in north-western Germany, after an employee was caught on camera poisoning a colleague's lunch, police said.

Police said they had arrested a 56-year-old man suspected of attempting to kill a colleague at the company in the town of Schloss Holte-Stukenbrock. They did not identify the firm, the suspect or the alleged victim.

The victim had noticed something suspicious in his lunch and notified his bosses and the authorities, police said. Video footage revealed the suspect spreading a powdery substance on the victim's food. Tests showed it was a poison that could have caused severe organ damage.

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

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.