The first alarm about the mass shooting reached the police on Tuesday, February 4. Over the next twelve minutes, the perpetrator Rickard Andersson fired 70 shots. Then he took his own life.
But the terror and the uncertainty for students, teachers and others who hid in school continued much longer.
SVT has talked to witnesses, sources, analyzed video and sound to try to understand what happened inside the school during the decisive hours.
See the survey in the video player above.