The main suspect in the Stockholm truck attack is an Uzbek construction worker and father-of-four believed to have IS sympathies, who went underground to avoid deportation from Sweden, police and reports said on Sunday.

Media quoted his colleagues as saying he was not "particularly religious" and that he "partied and drank".

Swedish dailies Expressen and Aftonbladet meanwhile named the man as Rakhmat Akilov and published his picture on Sunday.

Swedish police have only identified the suspect as a 39-year-old Uzbek national. He is accused of barrelling a stolen beer truck down a busy pedestrian street on Friday afternoon, mowing down shoppers before smashing into the facade of the Ahlens department store.

Four people were killed -- two Swedes including an 11-year-old girl, a British man and a Belgian woman -- and 15 others were injured.

The suspect was arrested Friday evening in Marsta, a suburb around 40 kilometres (25 miles) north of Stockholm.

According to sources close to the investigation cited by various media, the suspect, bloodied from the crash and with shattered glass on his clothes, fled the scene and ran into the nearby T-centralen subway station, taking advantage of the panic to blend into the crowd.

At 2:55 pm (1255 GMT), video surveillance cameras caught him in the subway system.

Sweden: truck attack Jochen GEBAUER, AFP, AFP

He took an express train to Stockholm's Arlanda airport, leaving a bloody trail all the way from central Stockholm, reports said.

He then picked up a bus from the airport to Marsta. His odd behaviour at a petrol station convenience store raised sales clerks' attention, who alerted police.

Police arrested the man at the wheel of a white van, various media reported, and placed him under arrest on suspicion of a "terrorist crime (by committing) murder".

Expressen reported Sunday he had allegedly confessed to the crime, telling investigators he was "pleased with what he had done" and had "accomplished what he set out to do".

- Gone underground -

Investigators have meanwhile remained relatively tight-lipped about the suspect.

According to police, he applied for a permanent residency permit in 2014 but was rejected in 2016.

"In December 2016, he was informed by the Migration Agency that he had four weeks to leave the country. In February 2017, the case was handed over to the police to carry out the order, since the person had gone underground," a senior police official, Jonas Hysing, said.

The suspect had been wanted by police since February 27 after not responding to a deportation order.

Swedish police say they have the suspected driver of the truck which crashed into a Stockholm department store, killing four, in custody Fredrik SANDBERG, TT NEWS AGENCY/AFP

Police said Sunday he was known to have "shown sympathies for extremist organisations" such as the Islamic State (IS) group.

According to Aftonbladet, Akilov had posted IS propaganda films on his Facebook account and "liked" an image of people covered in blood taken seconds after the Boston marathon bombings on April 15, 2013.

Expressen said several of his Facebook contacts were linked to the Islamist group Hizb ut-Tahrir.

On Sunday police said they had found components in a bag in the truck that could be used to make a "dangerous device".

- 'Partied and drank' -

According to press reports, police at the weekend raided an apartment Akilov had been renting for a couple of months in Varberg, a working-class suburb of Stockholm.

A father-of-four, he lived alone in Sweden, while his family remained in Uzbekistan, and worked in construction.

"He came (to Sweden) to work so he could send money to his family," a female acquaintance, whose name was not disclosed, told Aftonbladet.

Another woman who lived at an address where Akilov was also registered told Aftonbladet that he didn't come across as radicalised.

"He never talked about politics or religion," she said. "He didn't pray five times a day from what I know."

Pierre Svensson, who said he employed the suspect through a contractor for several weeks on an asbestos removal project in Stockholm late last year, described him as a "reserved person".

"He didn't stick out. He did his job. You can't say he was very sociable, we just told him what to do and he did it. He didn't speak much Swedish," he told AFP.

After losing his job at the beginning of the year, he had spent his days "smoking and sleeping", according to a former colleague.