A suspect who turned himself in is said to have confessed to carrying out the attack.

The authorities say the man, a 26-year-old Syrian, is suspected of being a member of the Islamic State group.

In the last few minutes, Germany's vice-chancellor has called for tougher knife laws in the wake of the attack.

Our correspondent in Berlin, Damian McGuinness, told us what we know about the suspect.

Yeah, quite a lot of details have been emerging over the night.

I talked to police earlier this morning and they told me that they confirmed that he is indeed a 26-year-old Syrian national.

They wouldn't confirm any other of the reports of whether he had come to Germany as an asylum seeker, which is being reported in some German media here.

But in a television interview this morning on German television, the interior minister of that region, Herbert Royal, said that the suspect had been living in refugee accommodation, which has since the attack been raided by police.

So there seems to be some sort of connection with that shelter.

There have been other arrests over the last 24 hours, which has led to a bit of confusion about who police think is the suspect.

Police have been really saying all along that they think just one person was responsible for this attack.

There was a 15-year-old boy who was arrested yesterday.

He, as we heard in that report, is thought to have known about the attack in advance.

He was heard to be talking about the attack before it happened.

So he's been charged with not reporting a crime to the police.

Police are hoping that he can give some more information about the attacker or the suspect and his being questioned by police right now as well.

So he might have some sort of connection possibly to the suspect.

The next stage now is that police are handing over this case to Karlsruhe, where the prosecutor general is.

And that is an indication that the authorities are now treating this as a terror-related act.

We've seen the flowers that people are leading and there's a church service today.

There is still a lot of shock in the city, isn't there?

That's right.

And this was supposed to be three days of celebration.

It was a three-day festival which started on Friday, supposed to be ending today.

Instead, it's a weekend of mourning and shock.

Right across that region, really, over the last 24 hours, festivals and festivities that were planned were cancelled.

Cafes were empty.

Restaurants were empty.

People were avoiding public transport because, of course, no one knew what was happening.

And there was a fear that the attacker was still on the loose and potentially dangerous.

It turns out that he appears to have gone straight into hiding.

Reportedly, he was hiding in a courtyard behind an apartment block near the crime scene.

And then he gave himself up to police late last night, saying that he was the attacker.

Now, of course, police have to investigate whether this is true.

And they're now questioning him and piecing together the evidence they have in order find out whether this suspect is indeed the man behind the stabbing.

Damian McGuinness, reporting from Berlin.