Speaking to CBS News Friday on her last day before resigning to become president of the University of California, Napolitano, 55, said, "Boston happened ... one or two people making what in fact is a low-tech type of improvised explosive device. That kind of attack has been a key concern of mine."
"What we can do is be always thinking about threats we could confront. There are no 100 percent guarantees in this business," she said.
His statement was met with loud applause by those attending, including current and former cabinet secretaries, law enforcement officials and Attorney General Eric Holder, CNN reported.
Napolitano's name was floated as a contender to fill Supreme Court vacancies in 2009 and 2010, filled by Sonia Sotomayor and Elena Kagan. Napolitano has been a U.S. attorney, state attorney general and governor of Arizona, but never a judge, CNN noted.