More than four years after Congress required the Department of Justice to assemble information about those who die in police custody, the agency has yet to implement a system for collecting that data or release any new details of how and why people die under the watch of law enforcement.

The information vacuum is hampering efforts to identify patterns that might lead to policies to prevent deaths during police encounters, arrests and incarceration, say advocates and the congressman who sponsored the Death in Custody Reporting Act.

“The result of it is that people are not coming home,” said Jesselyn McCurdy, deputy director of the American Civil Liberties Union’s Washington, D.C., legislative office. “They’re not coming home because they’re dying.”

The law, enacted in December 2014, is meant to paint a clearer picture of police-involved killings and deaths inside correctional facilities. It requires both state and federal law enforcement agencies to report information about those who die while under arrest, in the process of being arrested or while incarcerated.

The measure passed amid public outrage over police killings including the death of Michael Brown, an 18-year-old unarmed black man shot by a white police officer in Ferguson, Mo. Now, a crisis of suicides in jails across the U.S. — prompted in part by the incarceration of the mentally ill — has raised interest in the law and its delayed implementation.

Until the Department of Justice begins collecting this information, the public will have no way of knowing how many people are dying or under what circumstances, said U.S. Rep. Bobby Scott, D-Va., the measure’s primary sponsor. With the data, Scott said, “We can at least begin the discussion.”

The 2014 law renewed and expanded a measure that had expired eight years prior. It required the Justice Department to issue a report by the end of 2016 exploring how the agency and law enforcement could use the information collected to reduce deaths in custody.

No such report has been completed, however and advocacy groups worry the lack of accountability is letting law enforcement officials off the hook.

“Serving time in jail shouldn’t be a death sentence,” said Shannon Scully of the National Alliance on Mental Illness.

Late last year, the Justice Department’s inspector general’s office issued a review criticizing the department’s failure to move ahead. A string of bureaucratic hurdles caused the biggest holdups, the report found, most notably ongoing debates over what methodology to use to collect data. The report noted a new system isn’t likely to be in place until October at the earliest.

The agency has continued collecting some data about in-custody deaths under its old standards, but the Bureau of Justice Statistics, the Justice Department arm responsible for releasing it, is years behind.

Statistics through 2016 should be made public sometime this summer, spokeswoman Tannyr Watkins said. She blamed the delays in part on understaffing due to a hiring freeze from 2017 until April of this year. With the freeze now lifted, the agency “will expeditiously move to hire staff to fill the most critical positions,” she said.

Scott said the Justice Department needs to do better, whatever the reasons.

“I’ve just been disgusted that the executive branch can’t figure out how to require people to fill out these little forms on a quarterly basis,” he said. “It can’t be that complicated.”