The U.S. Supreme Court said Monday a Kansas man was improperly arrested and convicted for violating a federal law that required him, as a sex offender, to notify authorities when he moved to another country.

In this case, a registered sex offender who lived in Leavenworth, Kansas, moved to the Phillipines several years ago without notifying authorities of their decisions to re-locate.

The government claimed federal law required such notification. Both men were arrested and returned to the United States to face charges of violating the Sex Offender Registration and Notification Act, known as SORNA.

But a unanimous Supreme Court said Monday that sex offenders who leave the country could not be prosecuted under the law as it existed at the time. “SORNA's plain text … did not require Nichols to update his registration in Kansas once he no longer resided there,” Justice Samuel Alito wrote.