First, in my Dept, the other person would have been terminated. No question about it. The Sgt would possibly have been terminated, certainly demoted and transferred. No excuse for this type of behavior, at all.
As for shooting oneself through the hand with a Glock 40, I have never done it, but a guy who worked for me at ATS did, on my day off. He said it was VERY painful. The Hydrashok did a number on his hand, as well as the filing cabinet behind him. He was out for about 2 months in therapy. Same thing, attempting to dissasemble without removing the live round, and "press checking" the muzzle.
Another gent I knew, who worked security at a local vault, had fingers three on the left hand, with the trigger finger gone. Same thing, press checking a Glock prior to disassembly, without making absolutely dadgum sure the chamber was empty. The surgeon did an incredible job repairing the are, so it looks almost natural, even with the complete finger missing.
Is it the guns fault? No. Operator error. I don't like Glocks, and this is one major reason - they are expert's guns, not for the partially, or un-trained. Most PDs qualify as partially trained. Someone who knows the weapon intimately, and continuously trains on it, will do fine, while those who do not, would be far better served with a more traditional sidearm.