(NEW YORK) — In the two decades since the Sept. 11 attacks, forensic scientists have been hard at work trying to identify the 2,753 people who were killed at the World Trade Center — but the road hasn’t been easy.

As of this week, the Office of Chief Medical Examiner (OCME) in New York City has identified 1,647 victims, mostly using DNA from the human remains found at the site of the attack. But still, 40% of the Ground Zero victims haven’t been identified.

Mark Desire, assistant director of the OCME Department of Forensic Biology and manager of the World Trade Center DNA Identification Team, told reporters during a video call Wednesday that the investigation has been challenging, but after all this time, the team’s mission remains the same: to help the families of the victims find some closure.

Thankfully, new technology could help speed up the identification process.

“We’ve adapted, we’ve overcome and we’ve pushed that science, day after day,” Desire said.

Desire and other forensic scientists who’ve worked on the identification project said there are numerous factors that have made identification difficult. For starters, the remains at Ground Zero were exposed to several elements that can destroy DNA, including jet fuel, mold and fire.

John Butler, a fellow at the National Institute of Standards and Technology, who assisted with the World Trade Center identification efforts shortly after the attacks, told ABC News that it has taken a long time to get a manifest of all of the fatalities at the site, which included first responders, airplane passengers and crew, office workers and other civilians.

He noted that scientists had to gather as many DNA samples from the victims — whether it was from old toothbrushes, pieces of clothing or close family members — as possible to have a database to match the remnants found at Ground Zero.

“There wasn’t an inventory of everyone in the lab. They had to go out and get samples,” he said.

Desire also said there are victims for whom no additional DNA samples have been able to be retrieved.

“Maybe [the victim didn’t] have family or the family has accepted it and don’t want to be notified,” he said.

Over 22,000 human bone and tissue samples have been recovered from Ground Zero over the years, according to OCME. And by the end of May 2002, 736 victims were identified without DNA matching, according to a report issued by Butler a decade ago.

But he said one of the biggest issues that forensic experts still struggle with is the fragmented nature of the DNA recovered from the site, which is why he worked for months to come up with a new type of analysis for short tandem repeat (STR) markers in the DNA, which are unique among related persons.

“You can recover more information from a sample that has been broken into smaller pieces,” Butler said, adding that 20% of the identifications that have been made so far were done using the “miniSTR” tests that he helped develop.

Desire said the World Trade Center DNA Identification Team continues to work on analyzing the data they’ve gathered from the victims and making those DNA matches. On many occasions, the tests on a sample will match with a victim who has already been identified, but those matches still help in the long run, because it gives the team a more defined blueprint of that victim’s identity.

“It’s the samples we have gone back to over and over and over again,” he said.

Desire said his team is in constant contact with victims’ families — many who are still awaiting for their loved ones to be properly identified.

On Tuesday, for the first time in nearly two years, the office identified two victims. One of them is Dorothy Morgan, of Hempstead, New York, who worked for an insurance company at the North Tower. The identity of the second match is being withheld from the public at the family members’ request, OCME said.

Nikiah Morgan, Dorothy Morgan’s daughter, told WABC that she held out hope for years that “she was just out there somewhere.”

“I didn’t expect it after all this time,” she said.

Desire said he can’t give a timetable of when the next identifications will be made, but he believes new technology will lead to more matches.

The World Trade Center DNA Identification Team will soon be using a process known as next generation sequencing, which has been used by the military for long-term investigations involving unknown victims.

Desire said the technique has helped identify the remains of soldiers who died as far back as the Korean War.

“It allows us to look at samples that we had no hope in the past,” he said.

Overall, Desire said his team’s progress over the last 20 years has been remarkable, given the scope and conditions of the investigation. However, he said they’re still pushing to complete the identifications, for the sake of the victims’ loved ones.

“We won’t stop, because we know we can continue to make identifications,” Desire said.

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(CHICAGO) — A Black woman said she was walking out of a closed park in Chicago, adhering to police instructions, when a white police officer attempted to tackle her, allegedly unprovoked.

On Aug. 28, Nikkita Brown said the officer drove up to her as she was walking her dog in the Lincoln Park neighborhood of Chicago and told her to leave the area immediately.

Brown agreed, but the officer insisted on driving behind her as she walked out of the park, and eventually got out of his vehicle to follow her on foot, she told ABC News in an exclusive interview airing Thursday on “Good Morning America.”

Brown said she consistently told him, “I am leaving” and “I am walking away,” as she actively walked toward the exit.

The officer got out of his car and told her, “You can go to jail,” according to a video taken by Brown who recorded part of the encounter. Brown said he also allegedly told her she would never see her dog again.

Brown said she took her cell phone out to record the altercation and call for help.

“Even if somebody didn’t answer,” she said, she wanted to “at least leave a voicemail and say, ‘if you call me in the morning and you don’t reach me, I’m in jail, or worse.'”

The unmasked officer continued to approach Brown, ignoring her request to stay 6 feet away, videos show.

In one clip, the officer can be heard saying, “I don’t need a mask on, I’m outside,” shortly before attempting to tackle Brown, appearing to restrain her by kicking her legs and knocking her phone out of her hands.

After a 2-minute-long physical altercation during which Brown remained on her feet and screamed for help, Brown and the officer separated and both left the scene without the officer making an arrest.

“I knew if he got me on the floor, I would be dead,” Brown told ABC News.

According to the Civilian Office of Police Accountability (COPA), the group inquiring into the incident, the investigation is ongoing.

“We have a responsibility to investigate allegations of police misconduct and determine if they are well founded based on the facts and evidence of each case,” interim COPA chief Andrea Kersten said in a statement. “If violations did occur, COPA will hold the officer accountable.”

A Chicago Police Department spokesperson told ABC News that “the officer in question has been placed on desk duty as the COPA investigates the video.”

Brown said there were others in the area that night, and she felt profiled because of her race.

“I walked past four kids that were behind me… white males. As soon as I saw the car pull up, I looked behind me to see if he said anything to the kids. He didn’t,” Brown said.

At a press conference on Aug. 30, the CPD Superintendent David O. Brown said the investigation into the incident was opened in the Bureau of Internal Affairs and had since been transferred to the COPA.

If COPA determines that the officer violated a policy, a disciplinary recommendation will be forwarded to David O. Brown, at which point he is given the choice to agree or disagree with COPA’s recommendation, the superintendent said during the press conference. If he disagrees with COPA, the incident goes to the Chicago Police Board for adjudication.

The officer has not been identified yet due to privacy reasons, a COPA spokesperson said. Brown’s attorney, Keenan Saulter, is requesting the identity of the officer be released in order to file a formal complaint against him.

“There were other individuals in the park that night. So we still have to come back around to the question of ‘why her?'” Saulter said. “The worst scenario would have been that he writes her a ticket for being in the park after 11:00 p.m.”

The officer has allegedly been involved in previous cases of racial profiling, Saulter said, and should be fired from the force.

Now, Brown said she feels anxious leaving the house.

“If anything, I should feel even more protected by a police presence as a single woman walking at night, not be fearful that I’m going to die at the hands of an officer,” Brown said.

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(NEW YORK) — The last memory Scott Larsen has of his late father is eating breakfast together on the morning of Sept. 11, 2001.

He was only 4 years old when his dad, a New York City firefighter, left home for what would be the last time.

Joshua Powell, another son of a New York City firefighter who was in carnage of the 9/11 terror attacks, said he used to eat Cap’n Crunch with his father every morning.

Florence Amoako was eight months pregnant with her second child when she said goodbye to her husband as he went to work at the World Trade Center that day. Paulina Cardona, Katy Soulas and Lisa Reina were also pregnant at the time. Their husbands never made it home.

Over the past 20 years, ABC News has periodically gathered with this group of women who were pregnant when they lost their partners in the terror attacks. Their children, born after the attacks, grew up without meeting their fathers.

Our most recent gathering took place in late June of this year, where this group shared their perspectives on loss, grief and resilience.

Joshua Powell was 5 years old when his father, New York City firefighter Shawn Powell, was killed in the terror attacks.

“Although I was a kid, you realize one day, he’s not coming back, and sometimes when I was in class, I used to just look over at the door and in my head just imagine him walking through, and coming to pick me up to take me home. And nothing had happened, as if everything was OK,” Powell told ABC News.

Now at 25, Joshua Powell says he’s trying to make his father proud.

”I wanted to follow in his footsteps… I wanted to face danger fearlessly,” he said.

Powell said he didn’t become a firefighter because his mother was afraid to lose him the way she lost his dad. He has decided to pursue a career in medicine instead.

“Being a doctor, for me, or even being a surgeon, would be that same thing: running into the burning building. Running toward something that people are running away from,” he said. “Like when this pandemic happened, a lot of people were running away, but there were many people who ran toward it. I think that’s what I want to do.”

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