"An incredible number" of interviews have been conducted, as have several forensic investigations, according to Malena Rembe, Säpo's leading counterterrorism analyst.
"But because this person carried out the attack on his own, and isn't thought to have any connections to groups known to us, we've been forced to start from the beginning in order to survey him and his environment. That makes it extra time consuming and labour intensive."
Neither Rembe nor preliminary investigation leader Agnetha Hilding Qvarnström can reveal much more about the investigation because details remain classified.
However, more information has been promised when the investigation is complete, perhaps at the end of the year.
According to prosecutors no arrests have been in Sweden related to the case.
In Scotland, however, Ezedden Khalid Ahmed Al Khaledi, 30, has been in custody since March on suspicions of terrorist crimes which, according to media reports, include the financing of the Stockholm attack.
Abdulwahab blew himself up on Stockholm's Drottinggatan on Saturday, December 11th, in an event that jolted both the Sweden's intelligence community and the country as a whole.
In October, Sweden raised its threat level to "elevated" – the third level on a five-level scale, and it will likely remain there for quite some time.
It remains extremely difficult to assess the likelihood of a Islamic terror attack taking place on Swedish soil, according to Bertil Höckerdahl, head of Sweden's National Centre for Terrorist Threat Assessment (NCT).
"A terrorist attack could be imminent, or it could also be the case that it's ten, 15, or 20 years away. A lot depends on chance, luck or unluck," he told TT.
Suicide bomber Abdulwahab "came from nowhere", according to Sweden's top prosecutor, Tomas Lindstrand.
"It's not strange that we didn't know about him. To scrutinise all the billions of people on the internet is impossible. There he was just one of thousands of people with strange views," he told TT.
Lindstrand, who handles terrorism- and spy-related cases for the prosecutor's office, doesn't think Abdulwahab will be the last person to carry out a terror attack in Sweden.
"I think it could happen again," he said.
However, Swedish society hasn't undergone any major shifts and Prime Minister Fredrik Reinfeldt said the country's open and tolerant society has withstood the test.
"It's especially important to emphasise that because what he did to us was an attack on our openness and our freedom, which runs the risk of having people then treat one another with suspicion," said Reinfeldt.
"My impression is that we've passed the test, which is natural in a way because the consequences weren't any more serious than they were."