Answer :
First I would look back and think about reasons he would've been crying. Is something wrong at home? Did he get bullied at school? If I thought I had a reasonable answer I would go tell my favorite teacher at school. If it was a situation where I could actually help and be productive I'd probably go check up on him after school. If you never found a good enough explination for his tears I'd just let him be though. It's good to be concerned but when you don't have all the right information it could just make things worse. Hope this helps, but also what does this have to do with school?