We've seen it happen on school campuses, malls, even U.S. military bases. At times their victims are known and many times they are strangers, innocent victims who were simply at the wrong place at the wrong time.
The latest mass shooting struck midnight moviegoers at an Aurora, Colorado cinema.
Private Investigator and former NYPD Detective Steven Confino explains these tragic and shocking rampages can happen anywhere.
"It could happen with security around or without. Any public gathering type of area is a prime target," he said. "When you have someone that is willing to basically give his life to take others, you're really not going to stop him from doing what he wants to do. You can have five security guards in the theater, but if this guy knows the way to come in and he's armed with the right weapons, you're not going to stop him unless you know to look out for him."
He says, however, that people can't be afraid to live.
"Do I worry about my safety? All the time. Should everyone stay home and lock their doors? No, you have to live your lives," Confino says.
It's a message Licensed Psychotherapist Fran Sherman echoes.
"How can you live when all you think about is dying? If you walk around with the mentality that I'm not safe anywhere, you're going to live a very unhappy life."
Sherman, instead, explains why tragedies, such as the shooting in Colorado, should be reminders of life's good, not evil.
"Every day you've got to tell the people you love that you love them and live your life and be happy and treasure every moment. We never know what's going to happen. There's always going to be another sick person out there who might do some damage to somebody and we don't know but, can we sequester ourselves to our homes, no."
Experts also advise to always be aware of your surroundings and report anything or anyone who looks suspicious.