NEW YORK — On the morning of September 11th, 2001, Mark Desire rushed down the World Trade Center just after the first plane struck the north tower.

“The rumbling, it was the loudest, most violent time of my life,” said Desire. “That was a defining moment for me.”

It was his job to collect evidence for the New York City Medical Examiner’s office.

“That morning, it was all hands on deck, and our job was to preserve the evidence, so that means the victims, potential weapons, and pieces of the plane,” he said.

He was standing close to the south tower when it collapsed.

“I was running and thinking I’m going to make it through the door and then I got hit and I went through the window,” he said.

Desire jumped partially inside a nearby building; the debris crushed his foot.

“I would absolutely be dead,” said Desire if he hadn’t jumped to safety.

He still works for the medical examiner’s office 24 years later but in a new role. He’s part of a team that works inside a lab working to identify the remains of 9/11 victims.

“The families, if it’s a first-time identification, they’re kind of surprised that this process is still going on that we haven’t given up,” said Desire.

It’s the largest forensic investigation in U.S. history. One that started shortly after the towers fell.

The chief medical examiner at the time, Dr. Charles Hirsch, made the decision to preserve all of the DNA found at the site and to collect DNA from family members of the victims for comparison.

It’s that preservation that allows the current chief medical examiner to continue to carry out the mission today.

“This office made a promise to the families immediately following 9/11 that we would do whatever it takes for as long as it takes to identify their loved ones and return them to them,” said Dr. Jason Graham.

Forty percent of the victims still remain unidentified. That’s 1,100 people.

“The technology we have today wasn’t even a thought in anyone’s mind 24 years ago,” said Kevin McKenna, a criminalist working for the NYC Office of Chief Medical Examiner.

That includes a machine that they say has been a game-changer. It replaces what used to be done by hand.

“The machine has been one of the biggest advances we had,” said McKenna.

The samples undergo a chemical process that allows them to extract more DNA from more cells from even the smallest of samples. Scientists demonstrated how the process works using animal bones.

In addition, they’re reaching back out to families asking for new comparison DNA samples.

“There have been cases where individuals were infants in 2001 or 2002 and now they’re adults and feel like they want their samples tested to help with identification,” said Neha Desai, a criminalist with the NYC Office of Chief Medical Examiner.

Some of the samples retrieved from the World Trade Center site are so small, they’re waiting for even more advancements before testing them again.

“If we have a bone that’s only 1 to 2 grams, we only have in theory one chance left so then the decision can be difficult,” said McKenna. “Do we test this now with the technology we have now or do we wait until technology advances more?”

The work inside the lab won’t stop, until they can’t test anymore.

They say it’s not about getting positive results, it’s about giving families closure.

“This will go on, this mission will continue,” said Desire.

“I can tell you the scientists working on it, they were just kids back then but that commitment is as great today as it was back in 2001,” said Desire.

Not all of the victim’s families want to be notified of a positive identification.

An anthropologist works with the families to determine if they want to be contacted and if the identities of their loved ones should be made public. The families can change their minds and update their status at any time.

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