I remember having to testify about 1.5 years after witnessing an industrial accident (several years ago).  In preparation, the lawyers tell you to be careful to answer the questions truthfully but not to divulge "extra" information.  They further counsel to avoid drawing conclusions based on anything you "think" you remember.  In actual deposition, I was very surprised at how fuzzy my memory really was with regard to exact details such as timing and order of events. 

However, in this case, it appears to me that the amnesia is extremely convenient and a complete load of horsesh**.