My Dad was a LEO back in the 40's and 50's, If that holster has a little stainless tab that hooks up under the trigger guard it's the same rig he carried back then on a Sam Brown belt. It was an early attempt at ensuring the BG's couldn't pull your Police Positive out of it's holster. It didn't take the big city bad guys long to figure out how to over-ride that safety feature. The swivel was so that he could swing the gun up while sitting in the cruiser. (A black and white '49 Ford)
He went to work for 20 years with 6 in the gun and 12 in loops on the holster (talk about slow reloads). Todays LEOS go to work with 15 in the gun and four mags of 15 each on their duty belts, some probably carry more I really don't know.
One thing I am sure of, that holster on a Sam Brown belt with a Colt Police Positive in the holster with 12 shiney rounds in the loops, that was the coolest looking rig I ever saw as a kid and set the stage for a lifetime romance with guns. The absolute highlight of my childhood was when I turned 13, my Dad let me shoot his "Police Gun", a moment I will never, ever forget. Or my Dad, God Rest His Soul.