My colleague Garance Franke-Ruta wrote earlier today about how questions about the two suspects in the Boston bombing are already influencing the debate over immigration reform. Watching the coverage this morning and early afternoon, it's a good time to remember that it's impossible to legislate all behavior. That makes it tough to draw a straight line from what we know about the Tsarnaev brothers to American immigration policy.

Foreign Policy's Josh Rogin reports that Dzhokhar Tsarnaev, the younger of the two suspects and as of writing the surviving ones, is a naturalized citizen -- not a resident foreigner, not an unauthorized immigrant, not someone who overstayed a visa. Meanwhile, journalists are talking to an ever longer string of his former friends and classmates. While it seems his older brother Tamerlan may have been an angry, isolated young man, Dzhokhar is repeatedly described as a friendly and affable. His acquaintances are uniformly shocked and confused, and they all say they never heard him say anything that would suggest radicalization or an inclination to terror.

People change, and their personalities contain more than even the closest friend can ever comprehend. There's no immigration screening process -- indeed, no psychological investigation -- that can plumb the depths of a person or predict how he might behave in the future. And it's virtually impossible to predict the future actions of children immigrating to this country with their parents, whether as refugees or for other reasons. How can you tell whether the 7-year-old you're naturalizing will turn into a furious religious zealot 13 years later? We hear time and again how terrorism suspects seemed well-adjusted and normal for years before suddenly becoming radicalized. It's common sense for immigration officials to carefully screen who's let into the United States and who becomes a citizen, but it's inevitable that they won't be able to stop everyone. (Remember how the 1 percent doctrine served the country over the last decade.)

This is the risk that we have to live with as citizens of a republic -- the realization that the government cannot, and should not, seek total control over all aspects of citizens' lives, including their security. As legislators consider potential changes to the immigration process, it would be unfortunate for Boston to loom too large in their thinking.