The suspect turned himself in and admitted to the crime, Duesseldorf police and prosecutors said in a joint statement on Sunday.
"The involvement of this person is currently under intensive investigation," they said.
The details provide a somewhat fuller picture of an account late on Saturday by a state official who announced on German television the arrest of the man that authorities had been searching for in the 24 hours since the attack.
The Islamic State group earlier claimed responsibility for the attack.
Eight people were injured during the attack in Solingen during a festival. (EPA PHOTO)
The extremist group said on its news site the attacker targeted Christians and that as a "soldier of the Islamic State" he carried out the assaults on Friday night "to avenge Muslims in Palestine and everywhere." The claim couldn't immediately be verified.
Der Spiegel, citing unidentified security sources, said the suspect's clothes had been smeared with blood.
The police declined immediate comment on the Spiegel report.
North Rhine-Westphalia Interior Minister Herbert Reul says it was a targeted attack on human life. (AP PHOTO)
Two men, aged 56 and 67, and a 56-year-old woman were stabbed to death during a festival, in what Chancellor Olaf Scholz described as a "horrific act".
Hendrik Wuest, premier of the state of North Rhine-Westphalia, described the attack as an act of terror.
North Rhine-Westphalia's interior minister, Herbert Reul, visited the scene in Solingen. He told reporters it was a targeted attack on human life.
Solingen, well known for its knife manufacturing industry, is a city of some 165,000 people.
The city was holding a "Festival of Diversity" to celebrate its anniversary. It began on Friday and was supposed to run through Sunday, with several stages in central streets offering attractions such as live music, cabaret and acrobatics.
Fatal stabbings and shootings are relatively rare in Germany. The government said earlier this month it wanted to toughen rules on knives that can be carried in public by reducing the maximum length allowed.
In June, a 29-year-old policeman was fatally stabbed in Mannheim during an attack on a right-wing demonstration. A stabbing attack on a train in 2021 injured several people.
The episode comes ahead of three state elections next month in Thuringia, Saxony and Brandenburg, in which the anti-immigrant far-right Alternative for Germany (AfD) has a chance of winning.
Agencies
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