Currently the holster design is being blamed as a contributing factor to this self-inflicted GSW. Personally, I think it's a faulty design and have approached my superiors requesting Serpa holsters be unapproved for duty use at my agency and not be allowed on our agency range.
https://abc13.com/hpd-officer-accidentally-shot-himself-during-training/5731671/
https://abc13.com/hpd-officer-accidentally-shot-himself-during-training/5731671/