A store clerk's curiosity about why Najibullah Zazi was buying large quantities of beauty supply products indicated that something about the transaction wasn't quite right — and it's an example of the kind of citizen vigilance that can combat terror, a police commander said Saturday.

Los Angeles police Cmdr. Joan McNamara cited this summer's incident as police chiefs meeting in Denver adopted a model for a nationwide community watch program that teaches people what behavior is truly suspicious and encourages them to report it to police.

Federal authorities allege Zazi, 24, tried to make a homemade explosive using ingredients from beauty supplies purchased at Denver-area stores. He has been jailed in New York on charges of conspiracy to detonate a weapon of mass destruction in a plot that may have targeted New York City. Zazi has denied the charges.