Too many innocent people die from this gargantuan mistake. It is almost like akin to taking a gun and shooting into a neighborhood; yes you might not hit anyone and be OK but you also might hit someone and kill them.
Now in terms of what he needs to do? He needs to make sure this never happens again. It is a mistake and it isn't our place to judge the human even though the act was really bad. I'm sure he is still a great guy who made a big mistake. Learn from it and get better.