i think in reality all you can do is give them both a good talking too and let them know you're angry and what it has cost you. Only you know in general how good they normally are in working for you and is it worth causing tension between them by blaming one or the other.
To a certain degree you have yourself to blame as well for not having a procedure in place when packing up for the day check list, letting it be known who is responsible for what etc.
Its just one of those things you learn by although an expensive lesson for you its probably one that will never happen again.
In my previous injection molding life my old manager was very good at making you feel guilty/bad for any mistakes made, he never really shouted etc or fired off warnings (but you knew he was fuming mad) just had this knack of making sure in yourself you didn't screw up again and he never held a grudge once it was dealt with it was forgotten about.
It kind of always made you want to do your best for him and you knew where you stood in that he was a decent guy but he was the boss and most people working there respected that .
Going by his post though never employ Spruce