It depends on why you're crying QD. If my house burns down, I may be weeping over it because the insurance policy came due last week and I forgot to pay it. Or I may be weeping because my cat got smoke inhalation in the fire or I may be weeping because I lost all of my personal mementos. This is why I would weep "over" something.
If I don't care about my house or personal mementos I might weep for my cat while she's getting better. I might weep for her pain or discomfort. If she had died, I wouldn't be weeping "for" her because she can not be the recipient of my sorrow - I would be weeping "over" her (weeping for my loss).
The same goes for your sample sentence. If the victims died, you can't weep "for" them - you would be weeping "over" their deaths.
By the way - I find the phrase "all wept in silence" odd. How does a group weep in silence?