WCBSTV reports: The search is on for up to a dozen terrorists, possibly planning an attack on the United States. The FBI is looking for those associated with Najibullah Zazi, one of three already under arrest.

Sources told CBS 2 on Monday the plot may have focused on mass transit.

As the three men made their first court appearances in Denver and in Brooklyn, law enforcement sources said they are still tracking a core group of nine to 12 people with knowledge of the alleged terror plot. And the plan to use homemade explosives to bomb one or more terror targets in New York City may just have been temporarily interrupted.

So far the trio under arrest have only been charged with lying to federal authorities. Queens-based Ahmed Afzali — once a police informant — is accused of double-crossing FBI investigators by warning prime suspect Zazi and his father that there calls were bugged. But Afzali’s attorney said his client did nothing of the kind.

Sources believe Zazi, an Afghan national known to have received training by al-Qaida, was at the center of a plot which may have been focusing on mass transit.

A cell phone video of Grand Central Terminal was found in Zazi’s possession, as well as computer files and handwritten notes about bomb-building.

During the raids last week in Queens, investigators found cell phones and new backpacks, which could suggest an attack similar to the 2004 train bombings in Madrid, where cell phones were used to trigger backpacks filled with explosives.

(Source: WCBSTV)