Hamburg - Before Friday's attack, which left one person dead and seven injured, the 26-year-old man had previously been documented as an Islamist, but not seen as dangerous, said Andy Grote, interior minister of the northern German city.
Grote added that the agencies that dealt with the man, a Palestinian born in the United Arab Emirates, must now be examined for whether they properly followed up on any potential warning signs.
An arrest warrant was issued Saturday for the failed asylum-seeker, who is currently being held on suspicion of one count of murder as well as five counts of attempted murder, a spokeswoman for the Hamburg prosecutor's office told dpa.
The man has not produced any information about motive or the sequence of events, said spokeswoman Nana Frombach, adding that he has given "no evidence" of being mentally unfit to stand trial.
However, while authorities are still unsure about what drove him to carry out the attack, there are clues pointing towards a religious motivation as well as mental health issues.
The motive behind the attack
He allegedly attacked several people at random with a kitchen knife at an Edeka supermarket in the district of Barmbek before trying to flee, and was arrested after bystanders managed to overpower him.
The suspect had come to Germany as a refugee in 2015. After previously going through Norway, Sweden and Spain, he came to the German city of Dortmund, from where he was sent to Hamburg and applied for asylum in May 2015, according to Hamburg interior official Bernd Kroesser.
German Interior Minister Thomas de Maiziere warned people not to jump to the conclusion that the suspect had committed the crime for religious reasons.
"We have to expect that jihadist ideology is being used as a reason or justification for deeds that maybe were carried out for entirely different motives," he said. "The actual motives could be part of the personality of the perpetrator."
Victims of assault
An eyewitness told dpa that the attacker repeatedly shouted "Allahu akbar" (Arabic for "God is greatest") as he held up the knife during the attack.
A 50-year-old man was killed, while one 50-year-old woman and four men aged between 19 and 64 suffered stabbing injuries, some of them severe. A 35-year-old man was also injured while overpowering the suspect.
Hamburg police later increased the number of victims to seven after a 29-year-old reportedly received abrasions in the incident.
The injured victims were all in non-life threatening condition Saturday.
Criticism of asylum policy
I mourn the victims of the gruesome attack in Hamburg," German Chancellor Angela Merkel said in a statement. "I send their families my deepest sympathy."
Merkel has come under criticism for her open door refugee policy, which saw a record number of migrants enter the country over the last years, mostly from war-torn Middle Eastern and African countries.
Over the course of a single week last July, Germany witnessed several violent attacks, two of which turned out to be terrorist acts claimed by Islamic State and three of which were carried out by young men seeking asylum.
In one of the July 2016 attacks, a failed Syrian asylum seeker who was set for deportation for more than a year blew himself up outside a music festival venue in the southern town of Ansbach, injuring 15 people.
Hamburg Mayor Olaf Scholz called the Friday's attack "malicious," adding that the alleged attacker was a foreigner whom authorities had tried to deport but couldn't because he didn't have the required documents.
"What makes me even more angry is that the suspect is supposed to be somebody who is demanding protection in Germany and then turned his hate on us," Scholz added.