I have found the NTSB report in the meantime:
https://www.ntsb.gov/investigations/...ts/AIR2210.pdf
Part of it reports: "According to Bell (the helicopter manufacturer), the upper-left tail boom attachment fitting has the highest tension loading of the four attachment fittings and is considered the most important of the four attachment fittings between the tail boom and the aft fuselage. The upper-left tail boom attachment bolt separated first, resulting in the redistribution of the load normally carried by the upper-left attachment fitting to the remaining three attachment fittings and the subsequent initiation of fatigue fractures on the lower-left attachment fitting. Based on preliminary analysis of the fatigue crack growth on the lower-left attachment fitting, it is possible that the fatigue crack grew over multiple takeoffs and landings..."
So it isn't a case of the tailboom separating as soon as the first bolt parted, as I was initially thinking was the case.