The word is negligently.

So a flight attendant in Philadelphia, with a CCW permit, forgot she had her revolver in her purse, and got caught with it at the airport's security checkpoint. That bit of carelessness got her arrested. It also cost her her permit, her gun, and probably her job.

A Philadelphia police officer then tried to unload the weapon and accidentally discharged it. It's really simple guys. If you don't know how to unload a particular firearm, leave it alone. If you don't pull the trigger, the gun won't discharge. So when you are unloading a firearm keep your finger off the trigger.

To the journalist who wrote this piece. The word you're looking for isn't accidentally. It's negligently. It takes an act of will, and in this case stupidity, to pull the trigger.

H/T to James.