He's doing a bit more than that.
For one thing he is a qualified expert.
Ms Marten has previously told jurors Victoria died on 9 January, but prosecutors allege she died weeks later.
Prof Fleming said a measurement of Victoria's foot length suggested she was not born prematurely and was about two to three weeks old when she died.
He added he could not confirm Victoria was eight weeks old when she died.
Prof Fleming said: "All the pointers suggest to me that she was much younger. The best fit is that she was two or three weeks."
He also stated it is highly unlikely she died of hypothermia.
He is rebuffing the prosecution case and is qualified to do so.
An witness called by Constance Marten's lawyers said he did not think her newborn died from exposure.
www.bbc.com