A knife-wielding man who randomly attacked people in a German supermarket, killing one person and injuring five others on Friday, was "known as an Islamist" who fled to Germany in 2015 and was on police radar, officials said.

The unidentified man, 26, had no identification paper aside from his birth certificate, was born in the United Arab Emirates and fled to Germany in 2015 -- when the country accepted an influx of refugees from the Middle East.

"He was a known as an Islamist but not a jihadist," Andy Grote, Hamburg's state interior minister, told Sky News.

Prior to arriving in Germany, the man made stops in Spain, Sweden and Norway. His asylum request was rejected last year after he was on police radar as a suspected Islamic radical.

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A friend had tipped authorities off to changes in the man, telling them that he stopped drinking alcohol and started talking about the Koran, said Torsten Voss, head of the Hamburg branch of Germany's domestic intelligence agency.

"We evaluated him rather as someone who was psychologically unstable than had clear Islamic extremist motivations," Voss said at a news conference.

The man slashed people with a kitchen knife at a store in Hamburg, injuring five people and stabbing to death a 50-year-old man.

It's unclear what the man's motive was in the attack as of Saturday, but officials believe he acted alone and had no indication that he was working with a network, Grote added. He remains in custody pending possible charges of murder and five counts of attempted murder.

An additional person was slightly hurt when she fell in the tumult, police said.

The Associated Press contributed to this report.