The young men started disappearing a few months ago, one by one, often with no trace. Prosecutor Rashid Ozdoyev suspected a dark conspiracy: Maybe the abductions were the work not of ordinary criminal gangs but of Russia's top law enforcement agency.

Then Ozdoyev himself disappeared. Shortly after he got off an airplane from Moscow, where he had delivered a report criticizing alleged abuses by the agency, the Federal Security Service, Ozdoyev climbed into his car, drove off and has not been seen since.

The case has sent a chill through the southern region of Ingushetia, already anxious because of the recent wave of kidnappings and violence. The search for the missing prosecutor has turned up nothing; the investigation has gone nowhere. No one at the security service has been interviewed. And some of Ozdoyev's nervous fellow prosecutors said they assume the security service snatched their whistle-blowing colleague to shut him up, yet they feel powerless to do anything about it.

"It looks like the special services took him," Mikhail Akhiliyev, a friend and fellow prosecutor, said in a hushed conversation in a corridor of the prosecutor's office building, where that is not the official theory. "Everybody says we don't know anything. It's like a wall. There's no Rashid."

A spokesman for the agency, known by its Russian initials FSB, disputed allegations that it was behind the disappearance. But that has not quieted suspicions, drawing new attention to the evolving role in Russian society of this domestic successor of the KGB. The agency has been amassing new powers in the four years since its former director, Vladimir Putin, became president of Russia.

In places like Ingushetia, right next door to the war-ravaged region of Chechnya, the FSB increasingly operates with impunity, largely unchallenged by the local government, which is headed by a former KGB officer and Putin ally. At least 40 men have disappeared in the last six months, mostly members of the Ingush and Chechen ethnic groups, according to human rights activists who said they suspect involvement by the security service.

"We have a Bermuda Triangle here," said a stout bodyguard for another Ingush prosecutor, a handgun tucked into his belt. In reality, he confided, far more than 40 people have disappeared. He asked not to be identified: "We watch what we say. The less we say, the safer it is."

The only person who seems to be aggressively looking for Rashid Ozdoyev is his father, Boris, who is convinced that his 27-year-old son fell victim to the FSB and that no one else wants to prod too hard out of fear that they would be next. "It's absolutely outrageous," said Boris Ozdoyev. "The power of the FSB is enormous."

"How do they differ from terrorists?" he asked, complaining that FSB agents operate outside the law. "The only difference is they have a state krysha," a Russian term for "roof" that has come to mean mafia-style protection.

Boris Ozdoyev, 60, is no anti-establishment radical. A judge for two decades in Soviet times and later a member of Ingushetia's regional parliament, Ozdoyev and his family have devoted their lives to maintaining order in their oil-rich mountainous region. A second son is an officer of the FSB.

When Rashid disappeared in March, he had 10 years of government service and had risen to be the chief prosecutor's deputy. Working in a modest office at the end of the hall on the third floor of the prosecutor's headquarters, he had filed three reports sharply critical of the FSB in the previous six months, according to his father, who said he urged him not to do so for his own safety.

One of the reports -- a two-page memo sent to Col. Sergei Koryakov, local head of the FSB, late last year and reviewed by a reporter -- accused the agency of dropping the ball on investigating three explosions in Ingushetia in 2002. The FSB is sometimes accused of staging terrorist acts for political reasons, then covering up its involvement.

The most recent report, according to Boris Ozdoyev, was a 14-page paper outlining FSB abuses. His son delivered it to Moscow, then flew back to Ingushetia on March 11. He brought with him a DVD of "The Last Emperor" and planned to drive to the home of his friend, Mikhail Akhiliyev, to watch it. He never made it.

"We drove around, asking around. Nothing," said Akhiliyev. "No car. No him."

Boris Ozdoyev said his investigation into Rashid's disappearance points the finger directly at Koryakov. Ozdoyev said his other son found Rashid's missing car, a green Lada, covered by a tarp at an FSB garage, but it was later moved. Ozdoyev said he then picked up rumors that the kidnappers were FSB officers.

So, following the customs of local Ingush society, Ozdoyev and other male elders from his family convened a council meeting with one of the FSB officers and his relatives. At the meeting, Ozdoyev said, the FSB officer admitted involvement and said the operation was ordered by Koryakov.

"They staged an accident and stopped [Rashid's] car," Ozdoyev said. Then the abductors grabbed Rashid, stuffed him into another vehicle and drove him away while others removed the green Lada from the scene, Ozdoyev recalled the FSB officer telling the group. "He didn't know why. He was personally ordered by Col. Koryakov."

Musa Ozdoyev, 65, a retired economist and Boris's cousin, confirmed in an interview that he was at the council meeting and heard the FSB officer admit his involvement. "He was sitting in the [other] car. He said, 'I was playing the role of driver.' The others took care of the rest," Musa said.

Koryakov rebuffed requests for an interview in person or by telephone for nearly two weeks, saying he was too busy, but an FSB spokesman disputed that the colonel had ordered Ozdoyev's abduction. "If he ever did this he would be removed from his post immediately," said the spokesman, Alexei Baigushkin. He dismissed the allegations as propaganda by terrorists hunted by the FSB. "You should understand there are moments when terrorists use not only bombs but information channels."

The Ozdoyev case comes when human rights groups and local residents worry that the war in Chechnya, which pits local separatists against Russian troops and their Chechen allies, is increasingly spilling over into Ingushetia. More than a dozen people have been injured or killed, some summarily executed, in recent months, according to information compiled by relatives.

In early March, armed men stopped a car near the village of Altievo, pulled out the passengers and shot one of them dead as he crawled on the ground, then opened fire on another car that happened on the scene, killing a 24-year-old woman. The human rights group Memorial said it found evidence that the gunmen were FSB officers.

Then in early April a suicide bomber tried to kill the president of Ingushetia, Murat Zyazikov, by slamming an explosives-packed car into his motorcade, but Zyazikov was saved by his armored Mercedes.

The abductions seemed to mirror a pattern in Chechnya, where authorities have been regularly accused of seizing men in the middle of the night.

Bashir Mutsolgov, 29, was grabbed in December by armed men in camouflage and masks who jumped out of a car not far from his Ingushetia home, according to his brother, Magomed. Bashir has not been seen since, and his brother said contacts in the FSB told him their agency was responsible. "There are too many cases like this for it to be people in the wrong place," said Magomed, 30.

Mukhammed Yandiyev's son, Timur, 24, was taken away in Ingushetia in March by six masked men in camouflage. "If the ones who captured him know about some sort of crime, they should just tell me," said Yandiyev, 63. But after so much time, he said he fears his son may no longer be alive. "I'm beginning to doubt. Either they're being tortured somewhere in a basement or they're not with us anymore."

Authorities play down the problem, characterizing it as isolated. Zyazikov, the former KGB officer who is now president of Ingushetia, said in an interview that he knew of only seven reports of men disappearing. But he acknowledged that federal forces had sought to conduct zachistki, or cleansing operations, as they do in Chechnya, and said he had stopped that.

"We don't accept this. . . . We don't want to be in a war," he said in his office beneath a portrait of his grandfather, who once ruled the province as well. "We need stability, peace and mutual understanding."

Zyazikov, whose government has rebuilt schools, bridges and houses and sent sometimes reluctant Chechen refugees home, declined to comment on accusations against the FSB but said every disappearance is being investigated.

So far, the official investigation of Rashid Ozdoyev's disappearance has wound up in a dead end. The chief investigator, Nurdi Doklayev, said he could not rule out FSB involvement but could not interview Koryakov or other officers because the agency had disavowed any knowledge about the disappearance in writing. "I have an official answer from them that they don't have any information," Doklayev said. "How can I go to them when I don't have any evidence?"

Doklayev said he doubted Ozdoyev's reports would have inspired the FSB to kidnap him because they were not that important. "If we disappeared for writing reports there wouldn't be any of us here," he said. But he said that Ozdoyev's family, with a son in the FSB, should be able to solve the crime itself.

That's what Boris Ozdoyev is trying to do. With a wide array of contacts built up during a lifetime as a judge and legislator, he has found people who sell him information. He has been told his son had been held in Chechnya but was moved to another location last week.

"I'm looking for my son in all possible ways," he said. "I'm letting people know what's happening here to avoid creating a second Chechnya."

Boris Ozdoyev, right, a former judge and member of the regional parliament, is searching for his son, Rashid, left, a prosecutor who disappeared shortly after filing a report exposing the human rights abuses in Ingushetia.