Holder: New York Terror Plot Was Most Serious Since 9/11

Attorney General Eric Holder said Tuesday the alleged terror plot disrupted in New York was "one of the most serious in the United States since Sept. 11, 2001" — but he gave no indication when more arrests might be made.

In a question-and-answer session with reporters, Holder said prosecutors will bring all those involved in the plot to justice.

"There are people both in this country and also abroad who are committed to harming the American people and they're actively plotting to do so," Holder said.

So far, one suspect, Colorado shuttle bus driver Najibullah Zazi, has been charged with conspiring to detonate bombs in the United States. Zazi, who has denied any terrorist plotting, is being held without bond.

PHOTOS: Alleged NYC-Denver Terror Plot

Two other suspects, Zazi's father and a New York imam, have been charged with lying to investigators.

Court papers alleged that Zazi was plotting to build a homemade bomb, and law enforcement officials have said they feared such a bomb or bombs would be used to attack New York commuter trains.

The case came to light after Zazi drove from his Colorado home to New York days before the anniversary of the Sept. 11 attacks, prompting agents and police officers to conduct early morning raids on New York apartments looking for evidence of bomb-making activity.

Holder offered no new details of the investigation, but said the case has shown counterterrorism agencies succeeded in disrupting the plot.