But past year an evaluator who interviewed the Palestinian - who spoke fluent English, Swedish and Norwegian - said that while he had mental health problems, he did not pose an imminent danger, Mr. Voss said.
The Berlin newspaper Der Tagesspiegel said the knifeman was a known Islamist, but police did not immediately respond to the report. He was overwhelmed by passersby and slightly injured in the process, police said.
All of the injured are being treated or operated on in hospital, some of them with serious injuries, police said.
German police arrested the suspected attacker in the Barmbek district after witnesses followed the man and alerted authorities.
On July 24, 2016, a 27-year-old failed Syrian asylum seeker blows himself up near an open-air music festival in the southern city of Ansbach, wounding 15 others.
Mourinho denies Chicharito was a target
In reality, Hernandez would have been a great signing for virtually any Premier League club this summer. Signing the former Manchester United star was a real no-brainer for West Ham.
The assault risks reopening a bitter debate over refugees two months before general elections, putting pressure on Chancellor Angela Merkel over her decision to open Germany's borders in 2015, letting more than a million asylum seekers in.
Mr Froehlich said authorities intend to ask that he be held in custody on suspicion of murder and five counts of attempted murder, but may seek to have him held at a psychiatric unit instead.
Earlier on May 21, at least 6 people were injured after a man attacked people with a knife and a bat at a park in Japan's Chiba prefecture, the police said. As he fled, he wounded another four people.
The clip shows the alleged attacker surrounded by three men walking slowly towards him.
"We continue to investigate every possibility", the police statement said.
Olaf Scholz, the mayor of Hamburg, said the attacker was "a foreigner who was supposed to leave the country", but could not be deported because he did not have the necessary identification papers.