Never seen that before. So what does that mean?
My guess is that the pre-autopsy (body alteration) team was the one that was originally supposed to perform the 'autopsy' at Walter Reed Army Hospital. Jackie wanted it to take place at Bethesda. The Walter Reed team came to Bethesda to do their 'job' (pre-autopsy) and brought their own towels—Army towels. After that, the official autopsy began. The pre-autopsy was done in Bethesda's old morgue, while the official autopsy, with the official team (not the Walter Reed team), was conducted in Bethesda's new morgue. Today, we have two sets of pictures of Kennedy's body, taken in two morgues where two different autopsy teams were at work. The Walter Reed team ensured that the injuries would align with the lone gunman scenario. The Bethesda team (in the new morgue), mostly unaware of this, conducted the official autopsy. The participants of the Walter Reed team remain unknown, but they left behind a clue: the Army towels.