Arrested just hours after Friday's attack, Akilov appeared in a special heavily-guarded high-security courtroom. Handcuffed and wearing a thick green hoodie, he kept his head bowed.
"Akilov confesses to a terrorist crime and accepts his custody detention," his state appointed lawyer Johan Eriksson said at a custody hearing in Stockholm.
Judge Malou Lindblom ordered Akilov to remove the hoodie and he complied, revealing dark hair with streaks of grey.
After Eriksson's statement, the judge agreed to the prosecution's request to have the rest of the hearing held behind closed doors due to the classified nature of information in the investigation.
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After about an hour, journalists were readmitted to the courtroom and the judge remanded Akilov in custody.
The four people killed in the attack were two Swedes -- a 69-year-old woman and an 11-year-old girl -- a 41-year-old British man, and a 31-year-old Belgian woman.
Eight people were still in hospital today, including two in a critical condition.
Friday's attack resembled previous rampages using vehicles in Nice, Berlin and London, which were all claimed by the Islamic State (IS) group.
IS has not claimed responsibility for the Stockholm attack, but Swedish media reports on Monday said Akilov had told investigators that he received an "order" from IS to carry out the attack against "infidels".
Swedish police have confirmed he had expressed "sympathies for extremist groups, including IS," but disclosed no other details.
The Aftonbladet newspaper reported that Akilov told investigators he was "pleased with what he had done".
"The bombings in Syria have to end," he was quoted as saying.
Deputy chief prosecutor Hans Ihrman refused to comment on the suspect's motive, while lawyer Eriksson would only say that his client had told police why he committed the attack.
The investigative news magazine Expo, which specialises in monitoring far-right activity, said Akilov's Facebook account before it was taken down on Friday reflected a "contradictory image."
It said Akilov had "liked" Buddhist and Mormon websites, and supported both Russian opposition politician Alexei Navalny and Prime Minister Dmitri Medvedev.
The group, which claims to be non-violent and says it wants to achieve its goals by peaceful means, aims to establish a caliphate in Muslim regions of Russia and ex- Soviet Central Asian states.
Court documents seen by AFP showed Akilov, who is facing a lengthy prison sentence, had requested that Eriksson be replaced by a Sunni Muslim, saying "only a lawyer of this faith could assert his interests in the best way". The court refused the request.
"A confession is not enough to be convicted of a crime, other evidence is needed to back this up," Ihrman told reporters at the courthouse.
Police have previously said they are sure the suspect is the driver of the truck, citing technical evidence and video camera surveillance.
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