Updated

Heckling at a hacker's conference didn't faze the head of the National Security Agency.

Army Gen. Keith Alexander remained unapologetic Wednesday in Las Vegas about methods the NSA uses to, in his words, connect the dots and go after bad guys who aim to kill people.

He told the tech-savvy audience in his keynote comments at the annual Black Hat conference at Caesars Palace that the ability to look for patterns in telephone and email communications has stopped terror attacks in the U.S. and other countries.

Alexander even drew laughter when a voice in the overflow crowd shouted that he should read the Constitution. Alexander said he had, and the heckler should, too.

He insisted that it wasn't true the spy agency listens to specific phone calls and reads emails.