The authorities have denied involvement, suggesting many of the deaths are at the hands of al-Shabab, an al-Qaeda affiliate based in neighboring Somalia.

"We do everything that happens within the fight against terrorism within the confines of the law,” said Mwenda Njoka, spokesman for the Ministry of Interior.

But parliamentarians representing the predominantly ethnic-Somali counties of northeast Kenya have said many of the victims are targets of a campaign by security forces.

The 2.3 million ethnic Somalis with Kenyan citizenship have been under scrutiny since al-Shabab began staging attacks in 2011 in this country of 44 million. Suspicions have grown more intense since an attack in September 2013 on an upscale Nairobi mall, which left 67 dead, and an assault on Garissa University College in northeastern Kenya in April, which killed 148 people.

The Kenya National Commission on Human Rights (KNCHR), established by the constitution, released a report in September documenting 25 extrajudicial killings and 81 "enforced disappearances” of ethnic Somalis across Kenya since al-Shabab attacked the Westgate mall.

A number of those who were detained were later released, and some recounted how they were taken to military camps or police stations and tortured while being interrogated about suspected links to al-Shabab. Bodies of several of the victims bore signs of torture, the report said. It said witnesses named at least 10 police and military entities involved in the detentions, although some other victims were taken away by men in civilian clothing driving unmarked cars.

The human rights commission is investigating more than 30 unexplained deaths and over 50 suspicious disappearances of ethnic Somalis that have occurred since the report’s September publication. Fifteen of the deaths occurred here in Mandera County, an area wedged between Ethiopia and Somalia in the far northeast corner of Kenya.

The cases offer a chilling glimpse into how seemingly ordinary citizens are suddenly vanishing.

There is Isnina Musa Sheikh, a 29-year-old mother who was picked up in December at her tea shop in the county capital, also called Mandera, and found in a shallow grave four days later. The government said she had been a cook for al-Shabab, although it denied having a role in her death.

There is Abdirizak Mohammed Hajj, also 29. The youth soccer coach and shopkeeper was picked up in October while watching TV in his rented room in Mandera town. He hasn’t been found.

And there is 22-year-old Abdi Bare Mohamed, who had recently finished school, and was nabbed after heading out for prayer. His body was found about 10 miles outside of town in September. Markings on his neck indicated he had been hanged.

All of them were picked up in daylight by men in civilian clothing, traveling in unmarked cars, according to witnesses. Some of the men covered their faces.

Locals insist everyone picked up is innocent. When confronted about specific cases — such as Sheikh’s — the government often says the individuals are connected to al-Shabab.

In Mandera, parsing the truth is particularly difficult. Families straddle the border, businesses and schools serve people on both sides, and tracing connections to al-Shabab is complicated. Attacks with improvised explosives occur regularly, and the governor, Ali Roba, has survived numerous assassination attempts.

Many people here live part of the year in Somalia, part of the year in Kenya. The Somali mobile network has a stronger signal here than Kenya’s networks.

Human rights activists suspect that security forces are willing to eliminate those whose loyalty they doubt.

"Their statement always starts like this: ‘Let us not forget we’re at war,’ ” said George Morara Monyoncho, the human rights commission’s vice chairman.

Nearly every time a Somali’s body is found in Kenya, Abdirizak Salim’s phone flashes.

The 35-year-old Mandera native lives in Eastleigh, a predominantly Somali neighborhood in Nairobi. By trade, he is a construction contractor, but the community knows him as the one who finds their missing loved ones.

He stumbled into the role last year by tweeting about his vanishing acquaintances. Families began calling him and asking for help.

"This is a daily occurrence that is happening to my community,” he said.

Today his WhatsApp chat history is a startling mix of prosaic messages with family and friends and photos of bloodied, bloated corpses sent by local authorities and human rights workers urging him to come investigate.

When a message comes through, he and a colleague drive to the county where the body was found, to identify it and notify the next of kin.

"Sometimes they are tortured, rotted, they stink,” he said. "It really disturbs you at night. You remember how the body looked.”

Salim has been making regular trips to Mandera to try to glean as much information as he can. Until recently, locals here kept mum, caught between al-Shabab and jumpy, suspicious Kenyan security forces.

But the release of the human rights commission report and grass-roots social-media campaigns have lessened the taboo. The arrival of this reporter prompted a slew of calls from families wanting to meet to talk about the disappeared. They came clutching identification cards and passport photos of the disappeared and dead.

Some of these disappearances and deaths could be the result of feuds with al-Shabab or criminal gangs, the researchers with the human rights commission acknowledged. But many of those detained were picked up in daylight, when insurgents are unlikely to move around the heavily policed area.

Kenya has a history of extrajudicial killings by police.

"We have that kind of legacy,” Njoka, the interior ministry spokesman, acknowledged, saying that it "becomes easy for [people] to believe” there is an official role. But he called such allegations "propaganda.”

A wave of crime in the 1990s and 2000s prompted the creation of a so-called "flying squad” police unit that shot to kill. In 2008, Kenya put down an ethnic gang called Mungiki with a police unit that killed suspects.

"This is the default setting for our country,” said Thuo Kinyanjui, an officer for the northeast with the national human rights commission, adding that "whenever we have such a problem, we have a special force that brutally [handles] such a situation.”

When President Obama spoke in Nairobi in July, he warned Kenya to respect human rights as it fought terrorism.

In recent months, the crackdown has eased some. Kenyan Somali policemen have been relocated to posts in their communities and a northeast native was given the top regional security post, improving the relationship with locals. But the killings continue. Some fear that abuses will only boost the popularity of al-Shabab.

"You’re more or less creating the next generation of disaffected youth — a conveyor belt of easy recruits,” said Abdullahi Boru, a Nairobi-based researcher with Amnesty International.

The reporting for this story was supported by the Pulitzer Center on Crisis Reporting.

By Ariel Zirulnick