One morning in March, Bangor police Detective Jeremy Brock and Officer Dustin Dow made their rounds. Two of their stops included the Ranger Inn on outer Hammond Street and a boarding house on Union Street.

Each week, Brock usually spends a day on such visits, checking that the 120 or so registered sex offenders in Bangor are living where they have said they’re living.

At the motel, the registrants they sought weren’t there. At the boarding house, the officers found a half-dozen registrants, most of whom were home and in compliance.

One registrant had moved from the second floor to the third but hadn’t re-registered. Brock sent him to the police station to change his address.

Occasionally, Brock finds that a registrant has used a fake address. Brock and Dow spent some time searching for 247 Center St., only to find no building with that number.

The detective rarely visits a registrant’s workplace.

During his compliance checks, Brock makes calls to the registry in Augusta to see whether his information matches state files. He maintains his own list, which is not public, with names and addresses of Bangor registrants.

Most often, they match.

“What we do ensures accountability,” Brock says. “As long as they are accountable, they can live their lives. A majority are no problem, but there are about 10 percent who have trouble turning their paperwork in on time.”

Brock’s routine is similar to actions other Maine police have taken since 2003, when the state’s sex offender registry first went online.

Then, as now, the online registry includes the name, birthdate, photo, town of residence, employer, college (if the registrant is a student) and the crimes for which they were convicted, whether in Maine or elsewhere.

Little has changed in the registry despite the events of 10 years ago, when two Maine men listed on the registry were murdered by someone they never had met in the early morning hours of Easter Sunday, April 16, 2006.

In the aftermath of the murders, Maine weighed questions of balancing the aims of the registry — protecting children from pedophiles — with the suddenly real prospect of having people who had served their conviction becoming targets of vigilante violence. Debate continues to this day.

Victims of sexual assault support online registries in the name of public safety. Experts and lawmakers say there is scarce evidence that registries serve to prevent future crimes. And registrants decry the listing as dehumanizing and isolating while also putting their safety at risk.

“The registry is an important piece to have in place,” Elizabeth Ward Saxl, executive director of the Maine Coalition Against Sexual Assault, says. “Every state has one, and if they didn’t, one state could become a haven for sexual offenders. The challenge is that we don’t have the research that tells us it significantly improves public safety.”

The online version of the Maine Sex Offender Registry was unveiled Dec. 1, 2003, and listed about 1,200 names of people convicted after June 30, 1992.

In announcing the website, then-Maine Public Safety Commissioner Michael Cantara noted, “it’s a violation of law to use the registry to harass anyone who appears in the database,” adding, “I think we can count on Maine people to act responsibly when given this information.”

By April 2006, when a troubled young Canadian named Stephen Marshall used the registry to find and murder Joseph Gray, 57, and William Elliott, 24, in their Maine homes, the two men were among 2,500 people listed.

Despite an extensive investigation, Marshall’s motive for the killings remains a mystery.

He crossed the border to visit his father in Houlton on Thursday, April 13, 2006. Then, either late Saturday or early Sunday, he slipped out a window with a rifle, two handguns and his laptop and drove away in his father’s silver Toyota pickup.

He stopped at the homes of four registrants before pulling into Gray’s driveway in Milo. At about 3 a.m., Marshall sprayed seven bullets through Gray’s living room window, killing him while his wife looked on in horror.

Five hours later, Marshall knocked on the front door of Elliott’s mobile home in Corinth. When Elliott answered, Marshall shot and killed him.

Later, Marshall apparently abandoned the pickup and rifle at Sawyer Arena in Bangor and then boarded a southbound bus at a downtown station.

At about 7:30 p.m, the police, scrambling to follow Marshall’s trail of clues, stopped the bus on a ramp leading to Interstate 90, a short distance from Boston’s South Station.

Marshall, sitting quietly about 13 rows behind the bus driver, shot himself with the same .45-caliber handgun he used to kill Gray and Elliott. On his laptop, Marshall had compiled a list of 32 names and addresses from the sex offender registry — including those of his victims.

Later, what came to be called “The Sex Offender Murders” sparked an emotional debate about the registry on how much information should be made public and for what types of crimes.

State Sen. Bill Diamond, D-Windham, was chairman of the Legislature’s Criminal Justice and Public Safety Committee after the Marshall murders. That committee reviewed several proposed changes to the criminal code and sex offender registry

The longtime legislator and teacher also introduced more than 50 bills dealing with sex crimes and the registry.

Maine’s initial registry was simple, he said. In 1992, the law required those convicted of gross sexual assault against victims under 16 to register for 15 years.

But over the years, said Diamond, the registry has evolved into a complex system that determines how long an individual must register based on the age of the victim at the time of the offense, the nature of the crime and when it was committed.

In 1992, when the registry was created, a conviction for one crime required an offender to register. Today, 83 state and about a dozen federal crimes require a person to be listed on the sex offender registry.

In his 2012 book about sex crimes and the registry, “The Evil and the Innocent,” Diamond wrote that what started as “a well-crafted law” in Maine had become “twisted with unrealistic expectations, cumbersome regulations and too many federal interventions.”

The most demanding of those, according to Diamond, is the Adam Walsh Child Protection and Safety Act of 2006.

Named for famed “America’s Most Wanted” host John Walsh’s child, who was abducted and murdered in 1991, the law required each state to use a three-tiered system that requires registration for 15 years, 25 years or life, depending on the crimes and ages of the victims.

It was implemented fully in Maine at the end of 2013, in all aspects but one. Maine’s registry does not list juveniles unless they were convicted as adults. Listing juveniles goes against the juvenile justice system’s goal of rehabilitation, according to Diamond.

Along with scope, the expense and reach of the registry has also increased over the years. In 2015, the Maine registry was visited 1.5 million times and 4.7 million searches were completed.

The registry’s personnel cost is about $250,000 per year, according to Matthew Ruel, who heads the Maine State Bureau of Identification. That funds a staff of four people at the Department of Public Safety who work full time with the Maine State Police and local law enforcement agencies to make sure sex offenders are following the rules.

Legal changes have caused the total number of registrants in Maine to fluctuate. In 2009, the Maine Supreme Judicial Court found a 2005 law making the registry retroactive to 1982 was unconstitutional. The court, however, did not address whether the registry itself was constitutional.

As a result, in 2010, people sentenced for crimes that required registration between Jan. 1, 1982, and June 30, 1992, were allowed to request their names be removed, dropping the total number of registrants from its all-time high in 2009 — 3,352 — to 2,956 in 2010.

Then, in a rare 4-3 decision in 2013, the court declared the registry was constitutional while also further narrowing retroactive registration. As a result, registration fell from 3,176 in 2014 to 2,841 in 2015.

Despite all the changes to the registry, the additional laws and increased enforcement, many observers say evidence the sex offender registry significantly improves public safety is lacking.

Last year, Andrew Harris, associate professor of criminology and justice studies at the University of Massachusetts at Lowell, was awarded a $1 million grant from the National Institute of Justice to study sex offender registration and notification systems and how they operate.

It will be the first comprehensive, national assessment of how registry systems operate, how the information is translated into the realm of public safety and how the information is used by law enforcement and the public.

“I’m not convinced that alone the sex offender registries have a uniform impact,” Harris said in an interview. “You have to look at registries as part of a larger context that includes treatment, probation, supervised release and community support.”

“I think the registries have value,” he added. “But their public safety impact is more subtle than people think.”

The impact on registrants’ lives is not as subtle, according to some.

Augusta attorney Jim Mitchell, who represented 43 men who sued and won over being listed retroactively, said though the courts have said being on the registry is not a penalty, “it sure feels like one to them.”

“Well-rounded, happy citizens typically don’t get convicted of being sex offenders,” Mitchell said. “So, you start with people who are already a little bit outside the norm, and then you brand them and you publish it on the Internet and they can never be anonymous.”

“They have a very difficult time getting work and finding a place to live and getting along in society,” he said. “The question in my mind is what benefit does the public get in bringing that pain and harm on them?”

Failing to register is a crime, with penalties — for repeat offenses — of up to 10 years in prison. Yet law enforcement says finding offenders who failed to register is largely the exception, not the rule.

Ruell estimated between 2 and 5 percent of registrants fail to follow the rules. Brock, the Bangor detective, said he usually issues noncompliant registrants a court summons instead of arresting them.

State and federal law require law enforcement to notify communities when a sex offender moves into a town or neighborhood, but notifications are handled differently.

Most large cities and towns consider the listing on the sex offender registry as notification. Some small towns take additional steps: East Millinocket police Chief Cameron McDunnah, for example, has gone door to door delivering fliers and put a notice in an area weekly paper to let residents know a sex offender has registered in town.

Some fear the registry can deflect attention from real dangers.

The list may give the public some comfort about dangerous strangers, according to Ward Saxl, but statistically these are not the people most likely to sexually abuse a child. About 80 percent of sexual assaults are committed by relative or another person the victims know.

“It’s much easier to focus on the few offenders on the registry in your town and not focus on the fact that your next-door neighbor, uncle, soccer coach may in fact be a sex offender who’s not on the registry,” she said.

BDN writer Nick Sambides Jr. contributed to this report.