On paper, the South Portland crime statistic is startling: The number of registered sex offenders tripled since 2005, according to a new city report on police staffing.

But South Portland Police Detective Reed Barker said the increase – from 13 to 40 – resulted from a state law change and not from an influx of sexual offenders into South Portland.

A new reporting requirement, adopted in 2005 by the Maine Legislature, expands the statewide sexual offender registry to include anyone convicted of a sex crime after Jan. 1, 1982. Previously, the date of conviction was after June 30, 1992.

“We’ve always tried to keep track of convicted sex offenders, whether they’ve had to register under Maine law or not,” Barker said.

Many offenders in South Portland who registered after the law went into effect have convictions that date back 15 or 20 years without subsequent offenses, Barker said.

Under state law, sexual offenders must register with police in the cities and towns where they live, work and attend school. The Maine State Bureau of Identification maintains a statewide sex offender registry, which is online and open to the public.

“The number of sexual offenders in South Portland changes from day to day,” Barker noted. “The person may be off somewhere else working or has found another place to live. They could be on probation and have gone back to jail.”

Last week, the number of sexual offenders had dropped to 28 from 40, Barker noted. South Portland police provide a link to the state’s sexual offender registry. (The Web address is http://sor.informe.org/sor/)

The public can search the Maine database by name, zip code or city. People can see the offender’s photo as well as access birth dates, workplaces, addresses and physical descriptions.

The online service is free. More than 2,900 people are on the registry. It is the state’s most highly visited Web site.

The Legislature enacted the new retroactive reporting requirement in September 2005, with local police agencies now noticing the effects of the change, Barker said.

Barker conducts background checks on every sexual offender who must register in South Portland.

The reviews include criminal checks with state and federal authorities, identifying properties the offender owns, making visits to the offender’s home and notifying landlords, schools and employers of the offender’s criminal background.

Barker also tries to retrieve the original investigative report on the offender’s sex crime.

Barker maintains South Portland’s own sex offender database. He conducts random checks to make sure that offenders have not moved or changed jobs without informing law enforcement agencies.

South Portland police may distribute flyers or notify residents by phone when a sexual offender moves to a neighborhood.

The department also does mailings, issues press releases and posts notices on the Internet.

“We have a variety of ways to get the message out,” Barker said.

The increase in registered sex offenders in South Portland, as well as the police work to monitor them, was just one part of a city committee report on staffing shortages and hiring needs at the police department.

The South Portland City Council plans to review a proposal to hire three new patrol officers by 2010.

Barker noted that sex crimes have become better defined under Maine law, increasing the number of convictions and offenders who require monitoring.

The retroactive reporting requirement that caused a spike in the number of sex offenders in South Portland and other Maine communities is being challenged in the courts.

Maine’s highest court ruled in September to allow a constitutional challenge to the law. Two of the nine justices suggested that registration has become an additional form of punishment, after the offender’s sentence has been served.

If the retroactive requirement is invalidated, the names of offenders who committed crimes between 1982 and 1992 could be deleted from the centralized list.

The name of a sexual offender stays on the registry either for 10 years or for a lifetime, depending on the conviction.

A sex offender required to register for life has had multiple offenses, a violent sex offense or a sexual offense involving a victim under 14. A 10-year registrant has had a single offense involving an older victim.

In 2003, the U.S. Supreme Court voted to uphold registry laws, concluding that registration was not a form of punishment but a public safety measure.

But this fall, the Maine Supreme Court noted that how the registry is used has changed since then, and could constitute an additional criminal penalty.

The court wrangling has not deterred some Maine communities from adopting their own ordinances to restrict the movements of sexual offenders.

Gorham has an ordinance that keeps registered sex offenders away from school property and daycare centers.

Westbrook adopted a broad ordinance that keeps registered sex offenders away from schools, day-care centers, public libraries, day camps and any public or private place frequented by minors.

South Portland does not have any such ordinance on the books, nor does it propose to add any.

“We’ve always had sexual offenders in our community. This is not new,” Barker said.

He noted that local restrictions sometimes have unintended consequences. Bans may force sexual offenders to move more often or not report their whereabouts. The result is to make it more difficult for police to track and monitor them.

In 2007, the Legislature adopted safe zones that keep people convicted of sex offenses against children away from schools and child care facilities. The law took effect in September.

When the Legislature convenes in January, it will take up 26 additional bills dealing with sex offenders. The bills range from residency restrictions to limiting an offender’s Internet access.