10 mm is .40 caliber, which is a pretty heavy bullet and he made two accurate shots, one to the chest, hitting the spine, and one to the head, also hitting the spine.
It was a special lead flat nosed , gas checked round too which is specific for hunting 200 grain which made this kill. 10-mm in FMJ/JHP runs from 135 gr to 180 gr which likely would not have done it. I carry 10-mm sometimes so I am very familiar with its terminal ballistics.