In a week that saw the defeat of Obama’s gun control legislation, we watched a stunning display of domestic terror in Boston. The pressure cooker full of nails horrified us but didn’t shock us. Accustomed to senseless violence, we merely wait for its next occurrence.

Without warning, the Boston Marathon became the kind of event the media dreams of: bombs going off, bodies mutilated, a campus police officer executed, a carjacking, robbery and a wild bomb-tossing chase with a 200-bullet gun battle. Newscasters drooled as they broadcast each suspenseful installment.

Any good prosecutor must establish motive for a crime. What would be the motive for two brothers to rain terror, pain and death on hundreds of people they didn’t even know?

Tamerlan and Dzhokhar Tsarnaev, one of whom was a naturalized American citizen, decided it was a good idea to inflict pain and devastation on other Americans for the sole reason of their being Americans. They told their carjacking captive they wouldn’t kill him because he wasn’t an American.

Nurturing a philosophy of hate through online resources, the Tsarnaev brothers were self-starters. They accessed bomb-making instructions and ordered supplies online. Ethnic Chechens, they never lived in their homeland or suffered injustice or oppression. They had no linkage to the Chechen cause or terrorist groups. Tamerlan and Dzhokhar were just enthusiasts who conveniently adopted violent philosophies to fit their own personal angst.

Murder in the animal kingdom at least follows the logic of survival. Indiscriminate acts of mass violence are more difficult to comprehend. Why would someone fly an airplane into a skyscraper, open fire on a captive audience of movie-goers or rampage an elementary school with military style weaponry?

Our government says it will delve deeper into the root causes of this phenomenon. Obama breathes down the neck of the movie industry and scientists analyze Adam Lanza’s DNA in an attempt to control the causes of people getting in a killing mode.

We want to understand the root causes because we’re afraid and want these things to stop happening. But what if the causes are unstoppable? What if the root cause of senseless violence is living in a senseless world, a world where courage and kindness coexist with hatred and atrocities?

You don’t have to look very far to find instances of injustice in the world: countries are invaded, oppressed and destroyed by war while millions starve to death. You don’t have to think very hard to recall a time when you or someone close to you was unfairly treated. Whether it’s personal or concerning the world at large, the world is a place of victims and victimizers.

Since instructions and supplies are readily available, injustices easily give rise to retaliation. Actions that were carried out by armies can now be accomplished by individuals: people among us, going to the same schools, shopping at the same stores and exposed to the same media us.

Are they like the rest of us? Are there individuals who simply aren’t endowed with the faculty of conscience? We call them “inhuman” because we can’t deal with the idea of being like them.

But they are human, physically and mentally, exposed to the same confusions and dissatisfactions we all are. Except they kill. No dogma, philosophy or personal turmoil can make someone kill if they don’t want to.

The thrill of the kill is an adrenaline rush like no other, as any game hunter can attest to. No gun measure, movie rating or self-esteem enhancement therapy can compete with it. The military is aware of the killer instinct and relies on it in times of war.

War is usually thought of as a state of open and declared armed conflict between states or nations. The art and science of terrorism has changed the nature of war as we’ve known it. Whether driven politically or personally, the skirmishes can break out on any street corner and afterwards, with the aid of surveillance cameras and personal devices, can be viewed from every angle.