I know this is, to put it mildly, a sensitive subject, but if spectators and marshals were allowed to be standing or sitting in an area where a crashing motorcycle was going to be heading straight for them, who is responsible? In the days when the TT had a different level of recognition the course was subject to FIM inspection, with riders' representatives having their say, and there should be an equivalent today. If not, or additionally, there should be ongoing stringent checks that nothing can be improved, nothing has been missed. The most knowledgable people should be involved in this, including sector marshals, travelling marshals, organisers and riders, and then must take the blame if they have got it wrong. I do not feel that flinging police enquiries around is appropriate - at least not until after an inquest, which would identify any possible culpability. Flinging mud around and muttering in closed rooms is never appropriate.
Marshalling at a major motor sport event is not a day out for babies, kids, uncles and aunts, grannies and grandads, with picnics and chairs and tables, programmes at the ready to mark down the results. That is what spectators do, and I believe that the riders that risk their necks should expect that every possible thing has been done, by a professional team, to minimise the risks to them, and to what they could cause in the event of an accident.
Although there has been a lot of muttering about the TT course licence for racers, it is more in the cost and detail that this looks wrong. it does seem right that riders should be able to show that they are fit and qualified, not just turning out for the most challenging races anywhere with nothing to show that they have the wide and current experience to safely take part. This means racing elsewhere, whether it be on Irish road circuits or mainland short circuits, and is no different to how we used to get and maintain an International licence back in the old days.
It is sadly true that it must be difficult to find sufficient marshals with similar experience, if for no other reason than costs for them in getting off the Island several times a year. IMHO, this level of qualification should be the minimum for senior marshalling roles.