A good detective puts himself in the mind of the criminal. Think about it, phiwum. Imagine if you were part of the Russian mafia or even a speznaz as of the era of FSU and not only were you resentful of perceived hostile foreign powers (Sweden, Estonia, the USA) smuggling out the state secrets of your beloved fatherland and you become aware that this is being done on a public passenger ferry; you have fired off at least two warnings to the western states concerned but it is still going on. So, you have the military and maritime knowhow to take action to put a stop to it. The fact of a thousand members of public and crew are on board is - you reason - something the western powers should have thought about, not your problem - so you move heaven and earth to stop the latest smuggling which you have been tipped off about. So you make darn sure that ship goes nowhere. You wait until it gets into international waters and then on the stroke of Swedish midnight - (Sweden, do you get the message?) - a series of three explosions go off at the bow side locks - did the one at the atlantic lock at the bottom fail? - but you don't know that the car ramp will also come off, do you? So you attach a mine via a mini submarine to the side or accidentally crash the submarine you had tracking the vessel. Job done.
Given the likely motivation for the above scenario, of course you have to look at the world's political situation. It would surely be no coincidence that the smuggling of FSU defence and space secrets happened at the fall of the Soviet Union. So as terrorism is essentially a political act, of course you need to examine the world at war as of the time of the outrage. In 1994 we had the Israeli-Palestinian conflict with massive US involvement, with Clinton keen to be seen as 'peacemaker' and still keeping a beady weary eye on the Kremlin, with its support of the baddie Iranians (caught redhanded selling them a submarine the same year).
John Major would have been the prime minister in the UK signing off the Estonia Gravesite Treaty together with the Baltic nations barring Germany.
Why won't the UK government let Paul Barney et al have the document setting out the decision to undersign, as per the Freedom of Information Act, decisions made by the democratic government being a matter of in the public domain for UK citizens? It will have been discussed. Major can't just sign off a sovereign legal document unilaterally without going through the proper channels of passing a White Paper and then a Bill through the House.
So yes, if the Estonia sinking was an act of sabotage then yes the political landscape of the day becomes salient and that landscape includes the Swedes on behalf of the USA smuggling Russian state secrets via public passenger transport, which ergo means the public has a right to know.