Lama Zopa Rinpoche recently did numerous prayers for all the victims of the shooting tragedy that occurred at a movie theater in Aurora, Colorado. Following this example, I did the same for the shooting victims, the families, and the also the shooter. One of the main prayers that Lama Zopa did was the King of Prayers. You can get a copy of it here. If you’re interested in doing other prayers and practices,  I think you could also look into this list, which is some prayers that Yangsi Rinpoche suggests for those that have died. Please also remember to dedicate the merit to all sentient beings.