PORTLAND – Maine’s sex offender law could be unconstitutional because it retroactively increases criminal punishments for people who’ve already completed their sentences for sex crimes, the state supreme court said Tuesday.

The decision, another setback for the sex offender registry, comes less than two years after a 20-year-old Canadian man killed two sex offenders in Maine after randomly getting their names from the state’s online sex offender registry.

Since the shootings, there have been legislative debates about the registry, including efforts to eliminate it altogether.

An anonymous John Doe sued after being notified – a week before the shootings took place – that his name had to be placed in the registry.

Kennebec County District Attorney Evert Fowle, a defendant in Doe’s suit, called the ruling “alarming” and said it could result in broad changes to the sex offender law.

“This is a very activist court that seems to think it has to assume the duties of legislating,” Fowle said.

In his lawsuit, the man argued that Maine’s Sex Offender Registration and Notification Act violated his rights by requiring him to register as a sex offender even though the law didn’t exist when he was convicted. The man served fewer than 70 days in jail in the mid-1980s for a sex offense when was 19.

His case was originally thrown out. But the Maine Supreme Judicial Court on Tuesday ordered the lawsuit to be reinstated.

State Sen. Bill Diamond, co-chairman of the Legislature’s Criminal Justice and Public Safety Committee, said the opinion “adds a whole new layer of concern” over the sex offender registry as it now exists.

“This opinion will certainly cause us to pause and take a look at what we have,” Diamond said.

In April 2006, Doe was notified that he had to register as a sex offender. He then filed a complaint against Fowle, the chief of the Maine State Police and the Kennebec County sheriff alleging that the retroactive portions of the law violated the U.S. and Maine constitutions.

Doe said that if his name went on the sex offender registry, his wife would leave him and that he had reason to believe he’d lose his job and his neighbors would attempt to get him to leave the neighborhood.

He said he was also in fear of being targeted for violence. Barely a week after Doe was told that he had to register as a sex offender, Stephen Marshall of Nova Scotia shot two sex offenders to death in Maine after getting their names from the state’s online registry. Marshall then fatally shot himself on a bus after it was stopped by police in Boston.

Maine’s first version of a sex offender registration requirement went into effect in 1992, with lawmakers passing various amendments since then. In 2005, the Legislature amended the law so all sex offenders sentenced as of Jan. 1, 1982, had to register as sex offenders.

A Kennebec County Superior Court judge dismissed Doe’s lawsuit, saying that his due process rights were not violated and that the law not unconstitutionally vague.

But in a 39-page ruling, supreme court justices ordered that the complaint be sent back to the lower court for further proceedings.

The majority opinion, agreed to by seven of the nine justices, stated that Doe should be given a chance to prove that the sex offender law is punitive.

“Doe should be given the opportunity to develop the record and to prove, if he can, the excessiveness of (the law) in relationship to its stated goal of protecting the public from potentially dangerous registrants,” they wrote.

A concurring opinion, written by Justices Donald Alexander and Warren Silver, was stronger in its wording.

Alexander and Silver wrote that amendments to the law over the years have retroactively enhanced criminal punishments by changing a 15-year registration requirement to lifetime state supervision and removing the opportunity for waiving the registration requirement upon a showing of rehabilitation or other good cause.

They further wrote the law exposes registrants to punishments “similar to the shaming and ridicule penalties of colonial times by identifying and targeting them on the Internet, subjecting them to the documented risk of retribution and vigilante violence.”

Furthermore, they wrote, the Maine Constitution’s Declaration of Rights protects the right of “pursuing and obtaining safety and happiness.”

“For lifetime registrants, the (sex offender law) takes away that possibility and the prospect of redemption,” they wrote.

Deputy Attorney General Paul Stern wouldn’t speculate on what the fallout might be from the opinion. The case first must be reheard in Superior Court, he said. “This decision did not strike down SORNA,” he said.

Doe’s attorney, James Mitchell, was out of the country and not available for comment.