He shot her using a two handed grip, sometimes known as the "Combat Grip". This is what I was taught in the USMC.
I always fired Expert, both with the Colt M1911A1 .45 semi-automatic and later with the S&W .38 Special (IIRC) revolver carried by pilots.
In addition to annual qualification, I carried the M1911A1 in combat in Vietnam and later when providing security for both Crypto Codes and Payroll. However, I was not "Trained Security", never having been an MP nor a Mall Cop.
Video of the incident was taken from the shooters right side, so the position of his thumbs is unknown. However, the fingers of his left hand are clearly wrapped over teh fingers of hi right hand.
