I am not actually in opinion with this. Cuz let's say if indeed
it is due to inadvertant carelessness, but if it caused subsequent
larger repercussions, such as terrorists gotten the arms, or a shot
fire at mac donalds or goldsmith shops, etc...people die
etc...who's gonna account for it or ultimately the source still
boils down to the lost rifle.
Same thing in civil suits, careless (might be inadvertent) driving
causes people to die (knock down accidents), or careless
construction worker never put chains properly end up the whole load
fell and smashed to his colleague causing instant death, careless
mah-pu-poh (rag collector) accidentally dropped a large TV from 6th
floor HDB etc.
And next thing, EVEN if IT is due to carelessness (inadvertent),
but IF the person is PERPERTUALLY careless due to his less than
care nature, bo-chap, etc, then some punishment may be good in a
sense, it may shake him up and bring him to senses the
repercussions of his actions, so that next time, after ORD, he will
NOT make even greater or deadlier mistakes. 
