Another part of the answer is public vigilance – ordinary people being alert about behavior that raises doubts about the intentions or mental stability of acquaintances. Again, this is an imperfect defense.
Some people who knew 19-year-old Dzhokhar Tsarnaev in school said that he did normal activities like sports and parties. “He was never a troublemaker,” one former teacher said.
The Boston case also coincides with growing public debate about three issues with big implications for prevention of violent crime and terrorism: Gun control, immigration reform, and civil liberties in an era of drones and databases of online information.
On firearms, this was a case where the alleged bombers used guns as well as explosives. One of four people killed in the bombing and its aftermath was an MIT campus police officer who was shot while in his car.
The Tsarnaev brothers exchanged gunfire with police during a chase and manhunt that ended Friday night.
This comes during a week when supporters of stronger background checks for gun purchases failed in a US Senate vote. The National Rifle Association and some others argue that Americans’ safety can be enhanced through a greater presence of armed “good guys,” including guards to prevent Newtown-style tragedies in schools. At the same time, many Americans want to see access to assault weapons restricted, and efforts to ensure that people with criminal records or diagnosed mental disorders can’t buy firearms.