Swashplate,
Given that the case is ongoing i'll limit what i'll say: the prosecution is being brought against the individual on the basis that he performed incorrect maintenance which resulted in the tailboom seperating and impacting with the MR. Willie is correct in that the CAA grounded all helicopters serviced by the company until it had reviewed maintainence records for each heli.
On a side note, and this has no bearing on the case as it was always going to prove fatal, it is likely that there were 3 individuals sat in the front, and that 2 of them were not belted in. They were thrown through the plexiglass on inital failure and subsequent impact of the tailboom with the rotor disk.