Story highlights Peter Bergen: A very telling indicator of future violence by a terrorist, FBI behavioral analysts have found, is what they term "leakage"

Bergen says those whom terrorists confide in may be peers, family members, authority figures and strangers

Focusing on "leakage" is a better way to combat terrorism than to clamp down on Muslim immigration, he says

Peter Bergen is CNN's national security analyst, a vice president at New America and a professor of practice at Arizona State University. He is the author of the new book "United States of Jihad: Investigating America's Homegrown Terrorists" from which this article is adapted, and a related HBO documentary, "Homegrown", premieres Monday.

(CNN) What organization has mounted the most terrorist plots in the United States since 9/11? The FBI.

As part of its key mission of trying to stop the next terrorist attack, the law enforcement agency has mounted more than 30 plots that were, of course, sting operations in reality.

Peter Bergen

Despite the FBI's efforts, some "homegrown" American terrorists still have managed to carry off lethal attacks in the States in recent years, in places such as San Bernardino, Boston and Fort Hood, Texas.

This has touched off political debate, particularly among Republican candidates, about how to safeguard Americans, including spurious solutions such as shutting off Muslim immigration (Donald Trump) and carpet-bombing ISIS (Sen. Ted Cruz). Neither approach is realistic, not least because lethal attacks by jihadist terrorists in the States since 9/11 have been conducted largely by American citizens, while ISIS is embedded in major cities in Iraq and Syria and so carpet-bombing would kill a great number of civilians.

In fact, the real lessons learned should come from the law enforcement agencies that have studied jihadist terrorists in depth. A very telling indicator of future violence by a terrorist, FBI behavioral analysts have found, is what they term "leakage."