There is Alfred, it has happened before where engineers were interviewed in relation to a crash ( in the US I think ) and on the basis of their testament, some of them were prosecuted, some if I remember over issues that arose but were unrelated.....
You cannot run an accident enquiry and expect people to give evidence to assist in determining the root cause of an accident, if that information will be used to prosecute those giving it...
It will never happen again, indeed there is a culture forming now where people will simply refuse to give evidence and the possibility from that will arise that the true cause of an accident may not be found and others may die needlessly as a result.