Mirza Monterroso, DNA program manager, collects a sample from a Guatemalan woman whose son is missing. (Katherine Frey/The Washington Post)

The relatives carried photographs, identification cards, anything that might help find the missing. Inside a red-brick church in the nation’s capital, in a small room near a sparkling Christmas tree, they opened their mouths so workers could scrape a sample of their DNA.

Three brothers, in black jackets and matching jeans, sought the fate of a sister who vanished in the Arizona desert two years ago. Maryland housecleaner Olga Gonzalez was searching for her daughter Mirna, who was 31 when she disappeared in 2013.

Their hopes rest with the Colibri Center for Human Rights, a Tucson-based nonprofit organization that is traveling across the country to collect genetic material from family members of the missing.

Thousands of migrants have died in drownings and of heat exposure and other causes over the past two decades after slipping into the United States from Mexico illegally. More than 1,600 bodies were found by the Border Patrol alone in the past five years. Many are unidentified.

Law enforcement officials who normally investigate cases involving missing people — and ensure that relatives’ DNA samples are sent to an FBI database in case human remains are found — often refuse to take reports on migrants, partly because it is unclear which agencies along the nearly 2,000-mile border have jurisdiction. In other cases, family members of the missing reside outside the United States, or are also undocumented and afraid to come forward.

Working out of a suitcase they call their mobile office, from left, Robin Reineke, Mirza Monterroso, Arturo Magaña and Ben Clark wrap up the day after collecting 19 DNA samples in Washington. They take samples from relatives of missing migrants to try to identify human remains found along the U.S.-Mexico border. (Katherine Frey/The Washington Post)

Until a year ago, Colibri's main focus was to take reports of missing people, create their own database, and help families search. But late last year the organization received a three-year, $865,000 grant from the Howard G. Buffett Foundation to start collecting DNA in spaces loaned by churches and other nonprofit groups nationwide.

“It’s ridiculous that it’s taken them so long to get sampled for DNA,” said Robin Reineke, the executive director of the Colibri Center, sitting in the lobby of the church in the District’s Takoma neighborhood. “It’s very painful to lose a family member, but at least they would know.”

Colibri calls relatives from its database and schedule appointments to take DNA at locations the group does not disclose publicly, to protect people’s privacy. The group has held clinics in San Francisco, Los Angeles, New York, Tucson and Phoenix, and Washington. More are planned for Chicago, Seattle, and the Carolinas.

They have collected more than 370 samples that led to the identification of 32 people this year, with 21 findings still pending final approval.

When they visited the District in early December, they got 19 more DNA swabs. Tests are free and confidential, and the names of those tested are not shared with police.

Buffett, the son of Warren Buffett, one of the world’s wealthiest men, said he is funding the effort because families deserve to know what happened to their missing relatives — regardless of how they crossed the border.

“It’s past the point whether they entered our country illegally or not,” said Buffett, who, in addition to directing the foundation, is also sheriff of Macon County, Ill. “If you lost a son or a daughter, or a mother, cousin, and you have no idea if they’re alive or not. . . . People need to know that.”

A poster titled “The Things They Carried” shows items found with those who died trying to cross the border. (Katherine Frey/The Washington Post)

Among those searching for answers at the D.C. church were the three brothers from Central America, who said they last heard from their sister in a phone call that lasted less than 30 seconds. She was lost, and her cellphone battery was running out.

Arturo Magaña, a Colibri worker, asked a series of questions in hopes of narrowing their search.

Did she wear sneakers? Converse?

Did she have tattoos? Earrings?

“You never ask that,” the oldest brother said with a sad smile. “You never think they’re going to get lost.”

In a gentle voice, Magaña told the brothers that they may never recover their sister’s complete remains. Many bodies have been buried in pauper’s graves in Texas; in Arizona, many bodies have been cremated.

Finally, Magaña asked them to open their mouths. He scraped the inside of their cheeks with a plastic stick resembling a nail file.

The samples would be sent to a private laboratory in Lorton, Va., to be compared with samples provided by the Pima County medical examiner’s office in Arizona, the main government agency working with Colibri to identify remains. The lab also has a few cases from Texas — a state that accounts for more than half the deaths discovered in recent years — and they hope to include more in the future. Bruce Anderson, a forensic anthropologist at the Pima County office, said Colibri and other nonprofits are “doing something that in a perfect world should be done by the government.”

Gonzalez, the housecleaner who came to the D.C. church, said she paid $2,000 about three months after her daughter disappeared to a caller who claimed to have her. After she made the payment, she never heard from the man again. And so she came to the church to have her cheek scraped.

“I feel I am going to have an answer,” said Gonzalez, who is also from Central America.

Those seeking loved ones can write down their thoughts and feelings in a binder provided by the Colibri Center for Human Rights, which collects DNA samples from the relatives of missing migrants. (Katherine Frey/The Washington Post)

Karen Flores, a young immigrant who lives in New Jersey, told a panel at the United Nations in October that she could not get law enforcement to help her when her mother, Nancy, a Peruvian citizen, disappeared in 2009 in Arizona after crossing the border.

She hired a private investigator, posted fliers, and interviewed witnesses herself.

When Colibri came to New York this year, Flores gave a DNA sample. Last week, the Flores family learned that the DNA matched a cranium found in Arizona. They wept, Reineke said, when she delivered the news.

“But they kept saying ‘Thank you,’ ” Reineke said. “ ‘Finally, we have answers.’ ”