A man who blew himself up in Stockholm was carrying three explosive devices and intended to kill as many people as possible, prosecutors say.
Chief prosecutor Tomas Lindstrand said police were "98% sure" that the man was Iraq-born Taimour Abdulwahab al-Abdaly.
Abdaly, 28, is believed to have died minutes after setting off a car bomb on Saturday. Two other people were hurt.
Seven US FBI bomb experts are heading to Stockholm to help the investigation, Sweden's intelligence agency said.
Although Abdaly was a Swedish citizen, he had been living in the UK.
British police have been searching a house in Luton, north of London, where Abdaly lived.
Mr Lindstrand said Swedish police were now trying to work out what the bomber's target had been before he blew himself up prematurely.
"He had a bomb belt on him, he had a backpack with a bomb and he was carrying an object that has been compared to a pressure cooker. If it had all blown up at the same time, it would have been very powerful," he said.
A car containing gas canisters blew up first in a busy shopping street in the area of Drottninggatan at 1700 local time (1600 GMT) followed minutes later by a explosion in a street about 300m (985ft) away that killed the bomber.
Abdaly was named as the registered owner of the car.
Mr Lindstrand said they believed the bomber had intended to kill "as many people as possible".
"Where he was headed... we don't know," he said.
"It is likely that something happened, that he made some kind of mistake [and] part of the bombs he was carrying went off and caused his death.
"This was during Christmas shopping in central Stockholm and he was extremely well-equipped when it came to bomb material. It is not much of a stretch to say he was going to a place with as many people as possible."
Mr Lindstrand said possible targets included the city's central train station or to Aahlens, a popular department store.
In a profile on the Muslim dating website Muslima, Abdaly said he was born in Baghdad and moved to Sweden in 1992, before arriving in the UK in 2001 to study.
He said he had got married in 2004 and had two young daughters.
"I want to get married again, and would like to have a big family. My wife agreed to this," he wrote.
Mr Lindstrand said Abdaly was completely unknown to Swedish security services before the blasts.
However, he pointed out: "He didn't live in Sweden; he lived in the UK. He left Sweden maybe 10 years ago."'Distorted view'
Meanwhile, British police have been searching Abdaly's house in Luton. His wife and children are reported to live in the UK, although their exact whereabouts are not known.
It has emerged that Abdaly had attended the Luton Islamic Centre but left after other members accused him of having a "distorted view" of Islam.
A Swedish news agency has released an audio recording apparently made by Abdaly, in which he says oppression against Muslims in Europe will not be tolerated.
He refers to drawings of the Prophet Muhammad and to the presence of foreign soldiers - including Swedes - in Afghanistan.
If confirmed as a suicide bombing, the attack would be the first of its kind in Sweden.
Sweden's Prime Minister Fredrik Reinfeldt has said the attacks are unacceptable in Sweden's "open society", which he said was a democracy that respected different cultures.
The blast appears to have been of the same relatively unsophisticated nature as recent attempted attacks in New York, Glasgow and London, says BBC security correspondent Nick Childs.
Such attacks, carried out by individuals, are especially hard for the security agencies to trace and are an increasing cause for concern, he adds.
Sweden has had a narrow escape. If last weekend's suicide bomber's plan had worked, his multiple explosives would have caused mass murder amongst Christmas shoppers in Stockholm.
Swedish investigators have concluded that the Iraqi-born bomber, Taimour Abdulwahab al-Abdaly, had three devices and was probably aiming for maximum casualties.
In the event, he triggered two explosions - a car bomb and one on his body - but he was the only one to be killed.
Pointing to the fact that the second device went off in a relatively quiet street, Sweden's chief prosecutor Tomas Lindstrand said it had probably gone off prematurely.
"He had a belt, he had a rucksack and he was carrying something and all these three things were bombs. And probably he did something by mistake.
"And it's a qualified guess, I think, that he aimed to explode these bombs where there were many people gathered," he said.Attack preparation
Abdaly appears to have been unknown to the authorities in Sweden. He emigrated there from the Middle East in 1992 then moved to Britain in 2001.
He does not seem to have been flagged up in Britain as being of any particular concern, despite being effectively evicted in 2007 from the Luton Islamic Centre by his fellow worshippers who challenged his violent, extremist views.
But no-one reported him to the police and no-one in authority, it seems, detected his extremism from his postings on the social networking site Facebook.
Despite the fact that he was the only one to be killed by it, his attack would have taken careful preparation and planning.'Lone wolf' scenario
It is similar to other failed attempts by jihadists to kill citizens in London's Haymarket and in the US.
In a farewell message Abdaly boasted of going to the Middle East "for jihad".
Investigators are now focussing their attention on whether he was a "lone wolf" operator or whether he may have had accomplices in the UK, Sweden and elsewhere, making him part of a wider network with possibly more targets planned.
An Islamist website has already hailed him as a martyr, denying that his attack was a failure, and claimed that he acted to fulfil a pledge made to the Islamic State of Iraq, al-Qaeda's affiliate in Iraq, to punish Sweden for sending troops to Afghanistan and for allowing the publication of a cartoon insulting the Prophet Muhammad three years ago.