The admitted Norway killer traveled in and out of New Jersey for a week in 2004, a U.S. government official said Monday.
Anders Behring Breivik went to Newark, N.J., at the end of July 2004 as a tourist, said the official, who spoke on condition of anonymity to discuss Breivik's travel history.
It is not known whether he stayed in Newark the entire time or traveled elsewhere during his weeklong stay.
Norway participates in a U.S. visa-waiver program, and therefore Breivik did not need a visa to travel to America.
The FBI has looked into Breivik's U.S. ties, including travel and family, and has not found anything nefarious, though the bureau continues to assist the Norwegians in their investigation.
Breivik admitted bombing the Norwegian capital on July 22 and opening fire on a youth group retreat to save Europe for what he called "Muslim domination," killing 77 people.