I agree that the suicide verdict should be watertight, and in terms of culpabaility in other scenarios, such as work related, it would be much more difficult to prove - duty of care is tricky to define and practise with regard to apparently non-vulnerable adults.
I just looked at the elderly couples article as I clocked it unfolding a while ago and I'm glad it's being re-visited, as the ability of the alleged perpetrators in each case to enact such violence from a purely practical point of view seemed dubious. I didn't realise there were up to ten couples involved now - hideous.
I know that neither murder suicide nor being the victim of a serial killer is palatable for relatives, but honestly, I'd want it thoroughly investigated over living with such a horrible thing in my head that my DF had done such a thing forever. Yes it does happen of course, and being elderly does not make a person immune to committing horrible crimes, but still......
Suicide can be such a grey area - just recently a potential murder case has collapsed because there wasn't enough evidence to prove murder, accident or other, yet there was alot of very dodgy financial stuff occurring that implied motive.
How police investigate needs a shake up IMO. On one hand you get a handy innocent suspect being hounded into jail, then you have other cases where wrapping up a case quickly might miss vital clues not immediately obvious. It's easy to believe that the police are motivated by a sense of fairness and justice for victims, but bureaucracy and funding issues may over-ride more thorough investigation.
It's all very messy and often tragic.