Really sad stuff! My thoughts go out to the families of the deceased.
I hope anyone involved in the sub is never allowed within a country mile of such things in the future. Never!
Questions need to be asked, but its a bit early to be declaring that. Afterall this sub did get to Titanic at least twice before successfully so in terms of the structural integrity of the unit it was there and able to do what they said it would. Questions need to be asked around the maintenance of the sub, and the understanding and testing of repeated instances of that hull design to those extreme pressures. We know it could get to those depths, but with it being carbon fibre and not steel, does the structural integrity hold over time.
We can jump to conclusions very quickly, but we also have to accept that things we do are tough from an engineering perspective. In many ways, the design of this sub is way more advanced and structurally sound than any plane or any space shuttle as the pressures it needs to withstand are much greater, and as we know from space travel, accidents can occur. Things on space shuttles can break down over time, rivets can come loose etc. Its the same with planes, things happen that are unforeseen. Its an unfortunate outcome of a business like submarines, space shuttles and aeroplanes that the most that we can learn about the design of these pieces of equipment are when they fail.