The Russian aim would not be 'to kill as many civilians as possible' - they had already sent a warning twice to MI6 and Sweden intelligence to cease smuggling FSU state secrets/space programs/military materiel using the Estonia public passenger ferry. This warning was revealed to a Swedish newspaper some six years before Sweden finally admitted it was true that it had done exactly that on two occasions [it admitted to] during Sept 1994.
Thus, if the Russian intelligence guys were tipped off it was still happening then who is liable and who has vicarious liability, if any?
Even under Criminal Law of England and Wales, you are allowed to assault, even kill, a burglar on your property. In the USA you can shoot them stomme cold dead on your lawn, fleeing. And the liability in law is 100% the person carrying out the original tort, with the latter deemed legally innocent.
Change the parties to 'Sweden' and 'Russia' and we can see why Russia might see sabotage as reasonable reaction to aggravated theft of it state secrets, given the two warnings, and given what we know of their propensity to exact revenge for perceived wrongs (for example: bumping off defected ex-spies, killing, looting and raping civilians in former Nazi German territories after WWII).