WASHINGTON -- It puzzles statisticians and has been called "disturbing" by John Feal, a Long Island advocate for 9/11 first responders, survivors and families.
It led Rep. Carolyn Maloney (D-Manhattan) to write a letter demanding answers.
It is the fact that as many as 90 percent of the victims killed in the Sept. 11 terrorist attacks a decade ago are still not on the Social Security Administration's list of people who have died.
And Social Security won't provide a definitive explanation for that gap.
Social Security compiles the list, called the Death Master File, to stop retirement and disability benefits for those who have died and to retire their social security numbers from use.
The government sells the file for $1,800 a year. Many banks and businesses use it to screen for identity theft or fraudulent use of social security numbers. Social Security officials say the list is 99.5 percent accurate.
But the Scripps Howard News Service, in a series on lapses in the list's accuracy, found an anomaly: it does not show the expected 3,000-person bump in deaths on Sept. 11, 2001.
A Newsday analysis found only about 370 of the nearly 3,000 terror victims are listed on the Social Security death file among those who died that day. Just 66 of the 500 Long Islanders killed on 9/11 are listed.
There are no indications the omissions have led to fraud, yet Feal said it's still disturbing.
"They should be on there," he said. Their absence shows the government "lacks compassion, it lacks respect."
Not listed, for instance, is Father Mychal Judge, the New York Fire Department chaplain. And there is no clear pattern of who's on and who's not.
Take the Haskell brothers, both New York City firefighters from Long Island who died at Ground Zero: Timothy is listed; his brother Thomas is not.
Social Security officials declined to be interviewed. Instead, they issued a statement that indicates they've never investigated the death file's gap.
"There are several possible reasons," the statement said. "For example, we are not allowed, by law, to re-disclose death information from certain states," it said. "Another possibility is that the death was not reported to us."
New York City's Health Department, however, reported the nearly 2,700 Ground Zero deaths to Social Security, said spokesman Sam Miller.
The city does have a confidentiality policy that bars Social Security from publishing the names on its death file unless it first verifies the death with families or other sources.
But families and funeral homes provide 90 percent of the names on the death file, Social Security officials told Congress.
New York City funeral homes say they regularly report deaths to Social Security.
After getting conflicting answers about the gap, Maloney sent a letter on June 28 to New York's state and city health departments and Social Security requesting an explanation. She has not received an answer.
To check a name against the Social Security Death Master File, go to http://ssdi.rootsweb.ancestry.com/cgi-bin/ssdi.cgi