Barbara Butcher had spent decades staring death in the face.In 23 years at New York City's Medical Examiner's Office, she investigated more than 5,500 deaths, including almost 700 homicides, and walked into some of the city's most horrific crime scenes.But not even the most horrific crime scene could have ever prepared her for the sheer magnitude and devastation of Ground Zero.What she saw in the aftermath of September 11, 2001, and the worst terrorist attacks in American history still haunts her 24 years on. The veteran death investigator was tasked with collecting tiny bone fragments from the rooftops of the buildings surrounding the rubble of the decimated Twin Towers.Those fragments were subjected to repeated DNA testing as Butcher helped oversee the painstaking effort to identify victims. Despite the process that is almost impossible to comprehend, the heartbreaking reality is that some of the families who lost a loved one still have nothing to bury.More than 1,000 of the nearly 3,000 victims have not been identified among the remains, and may never be.'So many of the things I saw haunted me,' Butcher told the Daily Mail.'I had never seen that much room, that much destruction, and I had never thought that there would be thousands of people trapped beneath, obliterated, killed. It was inconceivable to me.' Nearly 3,000 people were killed when Al Qaeda terrorists hijacked four planes, crashing two into the Twin Towers and one into the Pentagon on September 11, 2001 Barbara Butcher spent 25 years working at the New York City Medical Examiner's Office, including as a death investigator at Ground Zero after the September 11 terrorist attacksThe Twin Towers were struck by two airliners on September 11, 2001, and subsequently collapsed during the deadliest terrorist attack in US history.Nearly 3,000 people were killed when Islamic terrorists hijacked four planes, crashing two into the Twin Towers and one into the Pentagon. Passengers and crew aboard the fourth, Flight 93, fought back against the hijackers before the plane crashed in a Pennsylvania field.Butcher was in New Jersey when the attacks occurred, and she fought to get into the city and help her colleagues during the grueling recovery process.'That was enormously difficult, and what my colleagues did- clambering across that pile to find remains- was life-altering for them psychologically, and of course, there are the health issues,' she said.Butcher explained that during that time she was promoted to Deputy Director of the medical examiner's office and was in charge of the identification process.'For every single remains we brought back, they had to be tagged, examined by medical examiners and forensic anthropologists, and each remains was given a unique code,' she said.'That identification process was overwhelming, and it was miraculous.'She said that investigators sent families questionnaires with strange questions such as how long a loved one's toe was.'Anything that we could get that might possibly identify a person,' Butcher added.Of the 2,753 people who were killed in the Twin Towers, Butcher said that only 60 percent have had their remains identified. Of the 2,753 people who were killed in the Twin Towers, Butcher said that only 60 percent have had their remains identified'When I say remains, I'm not talking about whole bodies or anything that size; I'm talking about the fact that we are taking the tiniest bone fragments found on top of the roofs of the surrounding buildings, and doing DNA testing over and over,' she said.'Each time DNA becomes more sophisticated and better able to extract a profile, they retest the remains. 'However, that leaves approximately 1,100 people unidentified. 40 percent of those who died there were never identified. 'Their families have nothing to bury, and that, to me, is absolutely heartbreaking.'Butcher noted that all of the deaths from the attacks are homicides, including those captured in horrific images 'jumping' out of the burning building.'The terrorists murdered them,' she said.Sign up for the free The Crime Desk newsletter for more harrowing accounts of the worst crime scenes in history.