The makeshift memorial stretched on and on, piles of carnations beside huge bouquets of roses, brightly coloured teddy bears wedged in among the flowers and the occasional photograph of one of the many victims.

Around the corner of the huge Crocus City complex, the burnt-out remains of the concert hall stood black and ravaged against the sky.

An Orthodox priest burnt incense and led a small crowd in prayers which they sang in soft, mournful tones. Many wept.

This is the worst terror attack on Russian soil since the horrors of the Beslan school siege in 2004.

Then, the world of Islamist terror was more familiar than it is now.

Then, Mr Putin's attention - and that of his security forces - was fixed firmly on it, not that it helped save the children of Beslan.

"You cannot put it into words. It's horrible, it's a nightmare," one man told us. "For what? Why did they take these people?"

"Where were our authorities?" his companion said through her tears. "Where were the guards who walk the streets? We didn't see them here."

Round the back of the building, people who'd been at the concert on Friday night were returning to pick up their things, mostly overcoats left in the cloakroom as people fled.

"We heard shots, and then they got louder and louder and louder. And when I saw the staff running down the hall and behind the stage, I realised this was a terror attack," said Oleg.

"Then when we got to the first floor there were already people killed, many, many bodies. Groups of two, three, five people. When I turned to my right there were 15 people killed there."

Who was behind the attacks?

Oleg doesn't want to speculate on who might be responsible. "We now have a difficult situation in the country and my words might have negative consequences," he said.

Tatiana who had gone to the concert with her grandson was less cautious.

"I think there are some traces, since they fled to Ukraine, it means that they probably had some kind of route which means someone was waiting for them there," she said.

It is certainly the inference Russia's president was making in his first, terse statement on Saturday evening where he intimated that the suspects were en route to Ukraine and that a "window" was prepared for them at the border.

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That suggestion of a "Ukrainian trace" has fallen on fertile ground in wartime Russia where Ukraine has targeted military installations and towns and villages along the Russian border in response to the Kremlin's devastating onslaught on their country.

But there is a considerable distance between bombing oil refineries - even dare it be said the shelling of Belgorod with the occasional loss of civilian life - and the indiscriminate slaughter of 137 civilians at a rock concert.

Plus, Islamic State Khorasan has claimed responsibility and released footage from one of the attackers' mobile phones as they conducted their rampage.

"Perhaps there was some help from Ukraine," says Natalya who lives close to the Crocus Hall complex.

"But who ordered it, who is the sponsor of this terrorist attack? I'm guessing it's the West, either the UK or the US."

Asking if she'd heard about the US intelligence warning issued to Russia on 7 March about a possible terror attack and whether that didn't change her view, she said: "Of course I heard about it."

"I think that the United States is also divided into two camps: those who do not want terrorist attacks and those who sponsor it."