A college student was killed on a train in San Francisco . DA : " I have no idea why this happened, but it is not the first time that someone has been shot and killed by an unknown assailant while riding BART. But nobody seemed to notice until the blast goes off . " Nobody noticed the gun before the shooting , DA says .
A college student was killed on a train in San Francisco . DA : " I have no idea why this happened, but it is not the first time that someone has been shot and killed by an unknown assailant while riding BART. " Nobody noticed the gun before the shooting , DA says .