There was a third post mortem done; I'm not clear why & who instructed it & if the pathologist who conducted it could also be a witness.
You may be thinking of the Dr White that was mentioned.
Dr Delaney started the first post mortem on Chrismas Day and continued on Boxing Day. He did another on 31st December and observed a further one on 17th Jan which was conducted by Dr White
Then there was the post mortem done by Nat Cary at the request of the defence after which he released her body to her parents
From Rupert Evelyn
Examination halted 10pm Christmas day. Resumed 1pm Boxing day
From Julia Reid
Dr Delaney did further examination on 31 Dec and observed another on Jan 17 by Dr White
Pathologist Nat Carey cleared the return of Yeates' remains to her family on 31 January 2011
http://joanna-yeates.gonetoosoon.org/