As soon as it was submerged in a 40°, which was shortly after 01:00, instead of which the Swedish naval base was alerted a whole one hour later.
Given how fast the ship sank, the circumstances: networks apparently down, Channel 16 weak and interference, Captains of nearby ship having to use NMT mobile phones instead, zero evacuation of the passengers - and this cannot have just been the crew's fault, everybody was taken completely by surprise; you can hear it in the voice of the Europa Captain, 'Estonia, are you calling...Mayday?' - the JAIC should have investigated the possibility of sabotage instead of writing off all of these issues as just one of those things.