By Suzanne Le Mignot

(CBS) — We’ve now seen more than a half-dozen shootings like this in just the past few months.

President Obama calls it a pattern of violence unparalleled anywhere else in the world.

“We should never think that this is something that just happens in the ordinary course of events, because it doesn’t happen with the same frequency in other countries,” Obama said.

Scenes of sadness like those in San Bernardino have been playing out again and again. So why does it keep happening? CBS 2’s Suzanne Le Mignot spoke with an expert who says there are several reasons why acts of violence like this take place.

This mass shooting in San Bernardino, California was a calculated incident.

“The fact that there was a party, provided a greater opportunity for entry,” said Dr. Nancy Zarse a forensic psychologist at the Chicago School of Professional Psychology, specializing in the psychology of terrorism.

“There was most likely a grievance, a sense of injustice that had to be avenged, there was ideation, a decision that violence was the only means, there was gathering of information, then there was the gathering of means, the weapons, the getaway vehicle, the clothing and then there was the actual attack,” said Dr. Zarse.

Today’s mass shooting is the seventh high-profile shooting in the United States, in just the past few months. Among the incidents:

On June 17, a gunman leaves nine people dead in an historic Charleston, South Carolina church.

At Umpqua Community College in Oregon, on October 1, an assistant prof and 8 students are killed.

On November 27, three people are killed at a Colorado Springs Planned Parenthood.

This consistent pattern of mass shootings led President Barack Obama to tell CBS News anchor Nora O’Donnell, “There’s steps we can take to make Americans safer and that we should come together in a bipartisan basis at every level of government to make these rare, as opposed to normal.”

When asked how we should react to these shootings, Dr. Zarse said, “I think self-care, take care of ourselves. I think look at risk factors for violence. I think, if you see something of suspicion, report it.”

And Zarse says what America needs, is a renewed conviction, that this type of violence won’t be tolerated and everyone must work together, to stay safe. That includes mental health intervention.