The context of the following conversation is While others were fairly sure of their decision, Aubrey's idea caused a shadow of doubt in their mind.:
Aubrey says Don't you guys see that bloodstain over there in the picture?  The defendant couldn't have caused that if he was on the other side of the room..
The friend responds The defendant is definitely guilty.  They found his fingerprints at the scene!.
Aubrey responds But it doesn't make sense.  How was he in two places at once?.
The friend responds That blood could have been from a long time ago!  I still think he's guilty!.
Aubrey responds Nobody would leave a bloodstain on the wall like that.  It has to be new and if it is then there is some reasonable doubt that our defendant didn't do it..
The friend responds I guess I wasn't really thinking about it that way but I suppose you could be right..