As a teacher, you are the role model for your students, and especially in these serious issues, you need to remain strong and do the right thing.
I feel you should talk to your students and explain to them what happened and ask them for their imput. Especially if they have fears, it is good for them to talk about the event. They then find out that they are not alone. You can ask them why they think it happened, and what we should be doing, and other questions on that order. I would go on line to these different websites to get help on how to introduce the issue in class. But, after that I think it really depends on the response of the students as to how the conversation goes after that.
Through doing this all many can overcome fears or speak out about things that would have sayed inside and weighed heavy on them. You need to remember that the students have different views and backgrounds which will really effect the way they think if catastrophies like these.
I would end on a positive note by asking them how we can help and then choosing something that the class can work on together to help.

Karalyn