KATE SNOW (Off-camera) Okay, back to national security now, Marysol. And the wake, in the wake of the deadly attacks in Mumbai last week, officials here in the US are asking the question, are we vulnerable to the same kind of violence? ABC's senior justice correspondent, Pierre Thomas, has more.

GRAPHICS: TRAINING FOR THE WORST

GRAPHICS: COULD MUMBAI HAPPEN HERE?

PIERRE THOMAS (Voiceover) A heavily armed N.Y.P.D. S.W.A.T. team descends on a Brooklyn building during a hostage standoff. It's a training exercise, but deadly serious. Seconds later, other S.W.A.T. teams arrive in armored vehicles. They race into a building to confront the terrorists.

PIERRE THOMAS (Off-camera) Police say last week's deadly attacks in Mumbai is a painful reminder of why they must constantly train for worst-case scenarios right here in the US.

RAYMOND KELLY (POLICE COMMISSIONER) There are no - two hotels that are alike. Each one is, is a little different. So we want to work closely with the security directors to enable them to do everything that they reasonably can do.

PIERRE THOMAS (Voiceover) Hotels, restaurants, shopping centers, so-called soft targets where there are lots of people and relatively weak security. US officials fear in the wake of Mumbai, attacks on public buildings are likely to become more commonplace.

HARRY SKIP BRANDON (FORMER FBI COUNTER TERRORISM CHIEF) All authorities around the world are worried about now are the, is the copycat effect, whether it's a couple of deranged people or one of the local al Qaeda franchises, if you will, who will see this and say this was easy. We can do it, too.

PIERRE THOMAS (Voiceover) After Mumbai, many US cities are reviewing their emergency response plans. A new FBI homeland security bulletin, exclusively obtained by ABC News, describes recent intelligence about an al Qaeda training camp which taught radicals how to use small arms to attack soft targets. The bulletin also revealed that this year, European authorities recovered a terrorist training video that teaches how to use machine guns and explosives to assault public buildings. The training video was discovered just weeks before the horrific Mumbai massacre, which employed many of the same tactics. Using such tactics are likely to become more common, low cost, a high chance of success, and the possibility of international headlines.

HARRY SKIP BRANDON (FORMER FBI COUNTER TERRORISM CHIEF) The objective is to get publicity for the cause and to sway governments. So, the soft targets are inviting, almost too inviting.

PIERRE THOMAS (Voiceover) Police say getting intelligence before an attack is the only real way to stop terrorists. Anything less is almost certainly too late. For "Good Morning America," Pierre Thomas, New York.