I didnt know what to expect as a LEO joining this forum. What a great scenario you have posted.
Personally, in lieu of giving the subject a "coup de gras" as you step over him, make sure you in fact put at least two in him from the get go. Preferably in the head to insure he is no longer a threat...or citizen for that matter. As with everything we do, shot placement is key. Front sight, smooth trigger.
Now, if you only got one shot off and are unsure of his demise, then yes, hit him again after he's on the deck. Is he still a potential threat? Kick the gun as you go by as well. If you can remember all this with a 200 bpm pulse and adrenalin, good on you.
In the end remember the old saying, "its better to be judged by 12 than carried by 6."