Göranson said there was "no doubt" about the intrusion, and went on to present a list of evidence that the Armed Forces had gathered.
For example, they analyzed a photo taken by a private individual of a white mass on the surface of the water. Göranson said the white foam surrounding a black dot was the result of water being pushed out of a submarine vent. He also presented new images taken by Swedish military showing the tracks of a sub along the bottom of the sea-floor in the archipelago.
Göranson added that the sub featured in the photo may not have been alone, there could have also been other subs in Swedish waters at the time. He refused to say, however, where the tracks were found or when.
Radio Sweden asked whether the military knows what the foreign submarine was doing in Swedish waters, to which the Supreme Commander replied, "That would be pure speculation."
Prime Minister Stefan Löfven said at the press conference, "We don't know who is behind this, but it is totally unacceptable."
Löfven said that the government will set up a new defence council, which will include top government ministers, and that the government will also continue to inform the opposition, but now in a more formalised and regular way. He also underlined the importance of strengthening Nordic military co-operation. He also added that there is no acute threat against Sweden at the moment.
"We have already proposed to the Parliament that we will increase our expenditure for the defense," said Löfven.
On 17 October, the Swedish Armed Forces said in a statement it was alerted by a "credible informant" that foreign activity was taking place underwater in the Stockholm archipelago, and that it had decided to conduct an surveillance operation in the area. The hunt for evidence took over a week.