If there was cargo on board in the form of Russian military stuff, for example stuff loaded on trucks (doesn't even have to be a Soviet truck just an ordinary army truck designed to carry armaments hardware) and the ship sank six hours into its journey, Bildt is one of the first to be informed outwith the coastguards and rescue services, and he immediately panics and puts out a press release the cause of the sinking was something technical and he knows something has gone wrong. Fact is, the divers were more interested in finding a briefcase belonging to Captain Andresson (probably an old stalinist who was trained at a Russian naval school) yet astonishingly, not in identifying who the three bodies on the bridge are, (the captain and his first and second officers in uniform that would identify them) tells you what the captain had in his possession was of great alacrity for the Swedish navy divers to find, going to the wrong cabin the first time round.
Putin was the recent head of the KGB as of the fall of the USSR. Who knows what Anderrson had in his briefcase that was so vital to find and how come Andresson didn't take the May Day call? Whatever it was, we might not know unless it is declassified.