An autopsy is a scary thing for the citizen accused of a homicide.  This is due to the fact that performing an autopsy is a horribly destructive act.  Once you make an incision, it is there.  There is no healing.  Once you reflect back the scalp, then it cannot be put back together.  Once the brain is severed and removed, it cannot be returned.  All of the kings horses and all of the kings men cannot put the decedent back together again.

The difficulty in the modern way that we perform autopsies is that a poorly documented and/or poorly performed autopsy will lead to the irrevocable and irreparable destruction of evidence.  It cannot be meaningfully examined again as the body cannot be returned to its pre-autopsy state.  You only get one chance to do it right.

This has been a long time criticism of autopsies.  The scientific community is starting to acknowledge that there is a greater need to try to find non-evasive or less evasive alternatives to get meaningful and useful data.  This largely surrounds medical imaging techniques.