The deadline, which turned out to be false, sparked a nationwide manhunt for a suspect who was ultimately cleared of any wrongdoing.
The documents show Säpo believed the suspected attack would take place between November 17 and 21. They do not, however, specify what type of attack was expected or why Säpo zeroed in on a 22-year-old Iraqi man as its main suspect.
"The information police and prosecutors had to go on was from November 17 until 21. So it was, to put it mildly, a critical situation," said deputy chief prosecutor Hans Ihrman, who took part in the investigation.
Police detained the man on November 19 at a center for asylum seekers in the northeastern town of Boliden. He was released without charge three days later.
The operation, and media frenzy it triggered, were criticized, although Ihrman told Swedish Radio News that he would make the same decision if faced with similar circumstances.
"I can say without hesitation that I would do exactly the same again," he says.
Following the man's release, Säpo issued a statement saying there was doubt over the man's identity which took a while to confirm through official records.
The agency also noted how the affair illustrated "the dilemma faced by all security services, i.e. having to act without having the full picture."