OP, ignore dancingbear. There are some good posts on here by people who have been the victims of drunk drivers.
It's so easy to bluster about how other people's children are scum who deserve to be unemployed/dead. However, there isn't a single one of us who hasn't done something thoughtless, stupid, reckless, or (in the case of drunk driving) criminal. We all like to think that our children would "never do X, Y, or Z", but absolutely nothing is impossible, however much we try to make sure that they are decent citizens.
We and our children are mostly fortunate enough to 'get away with it', and are grateful that nobody is seriously harmed. In the case of the OP's son: he did a terrible, terrible thing that could have exploded the lives of numerous people. He's lucky that that wasn't the case, and it sounds as if he's unlikely to do this particular thing again. Which isn't excusing or minimising it.
The OP isn't excusing or minimising, either. She is, like the overwhelming majority of mothers, someone who has tried to be the best parent she can be. And her son has still fouled up. We can be as judgemental as we like, but it really could be any one of us writing her post.