Tokyo, Japan - Mohamed Fujita used to host religious study groups at his home that were open to all Muslims. But today he's afraid to invite strangers, in case they're police informants.

Extensive surveillance has put many people of his faith on edge, he says, sowing mistrust.

A native of Japan who converted to Islam more than two decades ago, Fujita was one of 17 plaintiffs in a lawsuit that challenged blanket monitoring of the country's followers of Islam. His name has been changed in this story to protect his identity, after police documents labelling him a possible security threat were leaked online.

"They made us terrorist suspects," he says. "We never did anything wrong - on the contrary."

Islam in the Land of the Rising Sun

Fujita's wife first noticed the couple was being followed by law enforcement in the early 2000s. He says he would go out of his way to cooperate with officers when they would occasionally approach him. But they eventually asked that he report on other members of his mosque and he refused.

Then came the leak in 2010 of 114 police files, which revealed religious profiling of Muslims across Japan. The documents included resumé-like pages listing a host of personal information, including an individual's name, physical description, personal relationships and the mosque they attended, along with a section titled "suspicions".

The files also showed by the time the 2008 G8 summit was held in Hokkaido, northern Japan, at least 72,000 residents from Organisation of Islamic Conference countries had been profiled - including about 1,600 public school students in and around Tokyo.

Police in the capital had also been surveilling places of worship, halal restaurants, and "Islam-related" organisations, the documents showed.

Within a few weeks of the leak, the data had been downloaded from a file-sharing website more than 10,000 times in more than 20 countries.

Fujita and the other plaintiffs, many of whom were originally from Middle Eastern or North African countries, sued in the hope the courts would deem the police practices illegal. Their lawyers said police had violated their constitutional rights to privacy, equal treatment, and religious freedom.

After two appeals, the Supreme Court dismissed the case on May 31.

The justices concurred with a lower court that the plaintiffs deserved a total of ¥90 million ($880,000) in compensation because the leak violated their privacy. But they did not weigh in on the police profiling or surveillance practices, which a lower court ruling had upheld as "necessary and inevitable" to guard against the threat of international terrorism.

"We were told we don't have a constitutional case," says Junko Hayashi, a lawyer for the plaintiffs. "We're still trying to figure out, how is it not constitutional?"

Law enforcement mostly ignored the case. One of the few public statements they made came at a United Nations human rights committee hearing on the matter in 2014. An official from the National Police Agency said "details of information-gathering activities to prevent future terrorism could not be disclosed", but that "police collected information according to the law", according to UN records.

Japan's rich Muslim past and present

Some have defended the surveillance of Muslims, including Naofumi Miyasaka, a professor at the National Defense Academy of Japan. He describes the data leak as "the biggest failure in the history of Japan's counterterrorism" because it would have hurt the ability of law enforcement to gather intelligence on potential threats through "mutual trust and cooperation between police and informants".

The Supreme Court decision generated few headlines and little public debate in Japan. Local media outlets had covered the legal proceedings by focusing on the leak of information, tiptoeing around the police surveillance issue.

The most prominent public figure to comment on the Supreme Court decision was NSA whistleblower Edward Snowden, who spoke via video linkup at a symposium on government surveillance in Tokyo on June 4.

"People of the Islamic faith are more likely to be targeted ... despite not having any criminal activities or associations or anything like that in their background, simply because people are afraid," said Snowden, who once worked in western Tokyo at a liaison facility between American and Japanese intelligence services.

"But in Japan, let's look seriously at that. The Aum Shinrikyo was the last significant terrorist event in Japan, and that was over 20 years ago," he added, referring to the 1995 sarin gas attack on a Tokyo subway that killed 13 people and injured 6,000 others.

"This wasn't a fundamental Islamic extremist group, this was a crazy doomsday cult that wanted to make their founder the new emperor of Japan."

Other observers have also questioned whether monitoring a particular religious group en masse is an effective counterterrorism strategy.

"Germany had a similar programme, and they investigated and maintained files on 30,000 Muslims in Germany and didn't find, apparently, a single terrorist among them," says Jeff Kingston, director of Asian studies at Temple University in Tokyo. "So it's not clear that this indiscriminate surveillance is useful."

Hiroshi Miyashita, a law professor at Chuo University who's an expert on privacy issues, says he believes the lawsuit was the first major legal case in Japan to focus on mass surveillance. However, he adds that a state secrets law that came into force in 2014 would shield the issue from scrutiny by the public and the courts in future.

"Even judges cannot access information" about police practices under the new law, he says.

Japan's newest and largest mosque opens its doors

The Tokyo Metropolitan Police and the National Police Agency declined a request to comment on the court decision, and would not confirm whether they continue to profile and monitor Japan's Muslim community.

But the plaintiffs' lawyer, Hayashi, who is Muslim, says she believes the surveillance has only intensified.

"It's a really, really difficult thing to deal with, especially for the kids growing up here," she adds. "The police have been dealing with them as future terrorists."

While the lawsuit wasn't successful, Fujita says he has learned from the experience. To him, the top court's unwillingness to weigh their constitutional arguments shows that Japan's judiciary isn't an independent branch of government.

And years after the police surveillance came to light, he says it continues to rob many Muslims of a sense of trust, which he describes as "the foundation of human relationships".