Before Scott Kopytko joined the New York City Fire Department, he worked as a commodities broker in the South Tower at the World Trade Center. On Sept. 11, he rushed up the stairs of his old office building, trying to save lives with his fellow firefighters before the towers fell.
"He went to work, and he never came back," says his stepfather, Russell Mercer.
Almost every morning, Mercer and Kopytko's mother take turns visiting the cemetery across from their son's old high school in the Queens borough of New York City. Under a young oak tree next to fading tombstones, they water pink flowers behind a small, square stone engraved for Kopytko.
"It's a place where we can go, me and my family, to talk to Scott. But there's nothing there," Mercer says. "We need some kind of DNA, some human remains, where you can go to and say, 'This is where Scott is.' "
Fifteen years after the attacks, families of 40 percent of the World Trade Center victims have not received any remains of their loved ones.
Death certificates have been issued for these 1,113 victims. That number does include some of the immigrants who were in the U.S. illegally and working in the Twin Towers during the attacks. An estimated 60 immigrants, mainly from Mexico and Central America, are still missing, according to Joel Magallán, executive director of Asociación Tepeyac de New York, which coordinated support for victims' families.
'You Feel That It's Not Real'
Many families are still waiting for the New York City Office of Chief Medical Examiner to identify remains collected after the attacks. They're mostly bone fragments, some small enough to fit inside a test tube.
"You feel that it's not real. Your mind can't accept the fact that this person died because there's no evidence of it," says Sally Regenhard, whose son, Christian, was a firefighter who died at the twin towers.
She remembers how search and rescue efforts eventually shifted toward a recovery mission for body parts at ground zero and the Fresh Kills Landfill on Staten Island, N.Y., where debris collected from the World Trade Center was sifted and stored.
"It was like, you know, being in the rain, in the misty rain, and then slowly, slowly as time went by, you realize it was less and less likely your loved one would be identified," says Regenhard, who keeps a statue of St. Anthony, the patron saint of lost things, by the front door of her home.
'As Long As It Takes'
Many of the remains were degraded by jet fuel from the hijacked planes and other chemicals released from the collapsed buildings.
"There was heat from the fires, water being poured upon them, rain, wind — the worst conditions that you can imagine for the preservation of DNA," explains New York City's Chief Medical Examiner Barbara Sampson.
But the medical examiner's office was determined.
"We made a commitment to the families to do whatever it takes for as long as it takes," she says.
That's involved pushing DNA technology to its limits, with 10 scientists still dedicated to testing and re-testing the remains to find matches to DNA samples from the victims or their relatives.
Family members learn about new identification through phone calls from the medical examiner's office. In recent years though, most notifications are to relatives who have already received partial remains. In August, 12 remains were matched with previously-identified victims.
"It's not like we're sitting by the phone anymore like we were years ago," says Jim McCaffrey, a retired New York City fire lieutenant who is still waiting for the remains of his brother-in-law, FDNY Battalion Chief Orio Palmer.
Palmer's family have buried a vial of blood he donated before Sept. 11, but McCaffrey says there is still a "strange, empty void" to not have remains.
"Every now and then, you'll hear about some family getting a call. Hopefully that will happen for everyone," he says.
'Never ... Put To Rest'
The last new identification was announced in 2015. But progress on other remains may be held back for years or more because current technology cannot make reliable matches with tiny DNA fragments.
"The event itself can never really be put to rest because there will always be remains that can't be identified," says Jay Aronson, author of Who Owns The Dead?: The Science and Politics of Death at Ground Zero. "There's almost this sort of a very American belief that technology will eventually solve all of our problems."
Aronson says this raises complicated questions like, where should the unidentified remains be stored?
They're currently sealed in plastic bags inside a repository next to the National September 11 Memorial & Museum, seven stories below ground — a location some families have been protesting against.
'You Have To Have It'
There's also the question of how long to wait for remains to be identified.
Michael Burke says he's made peace with the possibility of never recovering any remains of his older brother, FDNY Capt. William Burke Jr., who stayed in the stairwell of the North Tower to help office workers trapped inside.
"You don't believe that he just vanished, that he's just pulverized into dust," Burke says. "You believe in what he did that day. You believe that the soul of man is immortal and imperishable."
Families of other victims like Kopytko are holding onto hope.
"You have to have it. Once you give up, it's all over," says Mercer, who turned 69 in August.
If he can't attend a funeral for his stepson's remains in his lifetime, then he hopes his daughter or his 2-year-old granddaughter will get the chance.
"Somebody," he says, "will get something."