Dr. Spencer Reid:  These pieces of twine are all different length
Derek Morgan: And you 're just figuring that out ?
Dr. Spencer Reid: I think it 's by design ! Starting with the first victim , the lengths are 25 , 15 , 12 and 19 inches
Derek Morgan: Yeah , so what ?
Dr. Spencer Reid: If you convert inches to centimeters , you 'll have a _ 64 _ , 38 , 31 and 48 , the exact ages of all four victims ! I think I know what this is about !