For the devastated relatives who have to pick up the pieces of a life lost or suddenly torn apart, such uncertainty can be distressing, leading to anxiety and depression.

“Every family of a victim, every injured victim I’ve ever dealt with wants to know,’’ said Kathryn Turman, assistant director of the FBI’s Victim Services Division. “Sometimes the motivation is obvious. Other times it’s not. I think every human mind struggles to try to make sense of what’s often a senseless tragedy.”…

Jonathan Metzl, a Vanderbilt sociology professor who studies gun violence, said it’s important from a societal standpoint to ask why these horrific events take place, an exercise that can also be part of the grieving process for victims’ loved ones…

“In most cases we never know the answer,’’ Metzl said, “and in a way the narratives we hold on to are the ones that make sense to us, but they might not be the reasons why somebody would do something like this.’’