For the past 13 years at an unknown cost to taxpayers a federal program has failed to accurately track the number of Americans who die each year at the hands of law enforcement.

The Arrest Related Death program, by the Justice Department’s own admission, has failed to account for as much as half of law enforcement homicides annually, according to an internal report released last year and never previously reported until now.

In 2003, the federal Bureau of Justice Statistics, a division of the Justice Department, started the ARD program in response the Death in Custody Reporting Act of 2000. States are required to submit data to the program, which must include information about each death such as name, age, race, sex, and the circumstances of death.

Several states and the District of Columbia have not reported any data on arrest-related deaths despite being required to do so by law. According to the Justice Department, from 2003 to 2011, Arkansas, Louisiana, Maryland, Mississippi, Montana, Nebraska, Nevada, New Mexico, North Carolina, Oklahoma, Tennessee, Wisconsin, and Wyoming have, in several of those years, not reported to the program. Georgia has never reported to the program (PDF).

A 2015 Bureau of Justice Statistics report that took two years to complete notes that the program has “methodological limitations” because it relied on voluntary reporting from law enforcement agencies (PDF).

The program should have captured an estimated 928 law enforcement homicides a year, the authors of the report wrote, but managed to capture only 453 annually over a six-year period.

Because reporting is voluntary, the authors concluded, the numbers of law enforcement homicides submitted by states to the program do not reflect reality.

From 2003 to 2009 an estimated 42 to 55 percent of all police killings were reported by law enforcement agencies to states that then submitted the numbers to the ARD program, according to last year’s report. (Data collection for 2010 was handled by a contractor through a “competitive award,” Justice Department spokeswoman Kara McCarthy told The Daily Beast. McCarthy did not say who the contractor was, how much they were paid, or who has access to the data.)

The numbers only came closer to reality when, in 2011, researchers began using web searches. That year the program saw a 39 percent increase in the number of police killings recorded—from 496 in 2009 to 689 in 2011.

By simply using search engines to find media reports of law enforcement homicides and other arrest-related deaths, the program became more effective. Why it took eight years for the Justice Department to use Google is anyone’s guess.

What the program costs is another unknown. McCarthy said that in 2014 the program was funded out of a $26 million fund that covers several other data collection programs. When asked specifically what the ARD program has cost annually for the past 13 years, McCarthy provided partial information.

Between 2003 and 2011, state agencies have been paid roughly $730,000 by the Bureau of Justice Statistics to collect data on arrest-related deaths, according to McCarthy. Over the same time period, Research Triangle Institute, a nonprofit, had been paid just more than $830,000 for its data collection services with the latest contract ending in 2014, McCarthy said.

The authors of the report also concluded that the program could be improved by “providing incentives” to law enforcement agencies to entice them to submit data on arrest-related deaths. One such incentive already exists in the form of a punishment mechanism provide by federal law (PDF).

In 2014, Congress reauthorized the Death In Custody Reporting Act with an important addition: The attorney general could revoke up to 10 percent of federal law enforcement grants—known as Justice Assistance Grants or JAG—from states that failed to report police killings and other arrest-related deaths to the program.

There is no indication that this punishment mechanism has ever been implemented, and Justice Department officials have failed nearly a year’s worth of requests for information regarding whether or not JAG funds have been revoked in the 13-year history of the ARD program.

Recently, a group of 67 civil rights organizations, including the NAACP and the ACLU, wrote to Attorney General Loretta Lynch last month urging her to utilize the 10 percent reductions, The Guardian reported.

“The financial penalty is critical” to the program reaching a more accurate count of arrest-related deaths, the authors of the letter wrote.

But a reduction in JAG funds is not enough to incentivize states and law enforcement to work more effectively at capturing accurate data. The funds do not make up significant portions of law enforcement budgets, and are designed primarily for wishlist extras like body cameras, money for indigent criminal defense, and improving mental health services for those caught up in the criminal justice system.

Last year, $179.6 million in JAG funds were distributed to all 50 states, U.S. territories, and the District of Columbia.

Georgia, which has received $5.3 million in JAG funds so far this year, is the only state to have never reported data on arrest-related deaths. Wyoming, which has not reported data since 2003, has received more than $530,000 in JAG funds in 2016.

The Bureau of Justice Statistics has not publicly released any data from the Arrest Related Death program from 2012 onward.