AAIB and Police investigations
I would expect the following as quoted by the AAIB on their report applies
AAIB investigations are conducted in accordance with Annex 13 to the ICAO Convention on International Civil Aviation,
EU Regulation No 996/2010 and The Civil Aviation (Investigation of Air Accidents and Incidents) Regulations 1996.
The sole objective of the investigation of an accident or incident under these Regulations is the prevention of future
accidents and incidents. It is not the purpose of such an investigation to apportion blame or liability.
Accordingly, it is inappropriate that AAIB reports should be used to assign fault or blame or determine liability, since
neither the investigation nor the reporting process has been undertaken for that purpose.
Extracts may be published without specific permission providing that the source is duly acknowledged, the material
is reproduced accurately and is not used in a derogatory manner or in a misleading context.
Therefore, I assume that the police are carrying out an investigation themselves but may use if permitted the AAIB as an expert witness, if the matter does proceed to a court case. I doubt that another expert witness will be as reliable and will be able to carry out such a through investigation as the AAIB do.
Regarding interviews the Police may permit the AAIB to be present in the interview, as it will be recorded to allow the CPS to decide if they will prosecute if a criminal act has occurred. Alternatively, the police may request a copy of a signed statement from the AAIB confirming the details provided to them by the pilot.
I note that the AAIB report states 'no reported defects' 'aircraft appeared to respond to pilots input controls' 'max alt recorded was 2600ft amsl but this may not have been the peak altitude' but they still have to examine the aircraft, examine maintenance records, condition before the accident, operation of the aircraft plus investigate the ATC recordings, audio recordings from the cameras, footage onboard still to be analysed in more detail.
This means that there is no clear indication as to why it crashed as yet. They have not ruled out a fault with the aircraft or ruled out pilot error either.