WASHINGTON (AP) -- Homeland Security Secretary Janet Napolitano says she was unaware of an immigration case involving a Senate intern and registered sex offender before he was arrested in December.

Napolitano told a Senate committee Wednesday that she first learned of the case after The Associated Press wrote a story detailing the case last year.

Senate intern Luis Abrahan Sanchez Zavaleta, an illegal immigrant from Peru, was arrested in December. Sanchez is a registered sex offender in New Jersey and was working as an unpaid intern for Sen. Robert Menedez, a New Jersey Democrat.

Immigration and Customs Enforcement officials in New Jersey were set to arrest Sanchez in late October but were told to delay the arrest after superiors were told the case could generate "significant Congressional and media interest."