WASHINGTON - When Keith David Wilson walked out of a South Dakota prison in 1999 after serving his sentence for raping a child, he was supposed to be tracked for life.

But in late September 2005, Wilson packed a moving van in the middle of the night and headed to Utah, moving in with a girlfriend and failing to notify authorities, court records allege.

According to the National Center for Missing and Exploited Children, there are an estimated 100,000 sex offenders in a similar situation, who fail over the years to add their names or update state registries, essentially vanishing from the system.

For Wilson, that changed in December, when he was apprehended by a federal marshal and charged under a provision of the new Adam Walsh Act. Passed by Congress last summer, the law establishes a national sex offender registry and makes it a felony, punishable by 10 years in prison, not to update a registration when moving between states.

It is beginning to pay dividends in Utah and nationally.

Wilson is one of four offenders who have been indicted in Utah under the law since it took effect. He has pleaded not guilty and is scheduled for trial in June.

Nationally, 84 arrest warrants have been issued and 66 fugitives have been apprehended for violating the law, Attorney General Alberto Gonzales said in prepared testimony to Congress last week.

"I have always made this a very highest priority in my office because of two factors: One, Utah has a lot of children, and two, we have a very trusting citizenry, so those two factors make us a target above and beyond" what other states may be, said U.S. Attorney Brett Tolman.

Among the four offenders charged in Utah is John Henry Gill, whose arrest last October was the first in the country under the new law.

"Here in Utah, we jumped on board real fast," said Jim Phelps, supervisory investigator at the U.S. Marshals office in Utah.

Gill had been convicted in Idaho of possessing sexually exploitative material, but failed to update his registration when he moved to Salt Lake City until being arrested for trying to use a fraudulent Social Security number.

Phelps said his office has six more cases it is building now against individuals believed to be in Utah, but who have failed to register. And information is flowing between states and between the Utah registry officials and federal law enforcement.

Just this week, for example, he received a tip from Ohio law enforcement about a sex offender in Utah who has failed to register.

"Between all the different groups, everything seems to be coming together," said Phelps. "As time goes on, we're starting to get more and more cases. More individuals are being identified."

It took about two years for Congress to pass the Adam Walsh Act. Named after the slain son of "America's Most Wanted" host John Walsh, it was introduced closely on the heels of the murder of Jessica Lunsford, a 9-year-old from Florida who was kidnapped by a convicted sex offender, sexually assaulted and buried alive.

It had the backing of other parents who purportedly had fallen victim to sex offenders. Elizabeth Smart, who allegedly was snatched from her Salt Lake City home in 2002 and was missing for nine months, and her father, Ed, appeared alongside Sen. Orrin Hatch to urge its passage.

The Sex Offender Sentencing, Monitoring, Apprehending Registering and Tracking Office - the SMART Office - was named after Elizabeth Smart. It is headed by Laura Rogers, a prosecutor from California, who is developing guidelines to set uniform standards for various state registries.

"The Adam Walsh Act was a significant accomplishment," Hatch said. "I've had a lot of letters from Utahns about this - they want the guidelines done as quickly as possible. So do I, but I also know these things take time to get it done right. . . . I'm hopeful that [the Department of Justice] will publish them for public comment in the next few months, as promised."

But the biggest uncertainty is funding.

"The marshals have saddled up," said Walsh. "But the reality is this new Congress hasn't funded it yet, so U.S. prosecutors, pilot programs in every state . . . are all asking the same question: Show me the money."

Congress is in the process of setting the budget levels for next year. The Marshals Service alone has asked for $7.8 million to fill 54 positions to pursue sex offenders.

Before becoming a U.S. attorney, Tolman was lead counsel for the Senate Judiciary Committee and helped shape the law as it made its way through Congress. He says he is optimistic that there is a critical mass building to clamp down on sex offenders.

"I think that we're right on the cusp of getting enough partners and enough people motivated on this that we could make a very significant difference," Tolman said.