A group of congressional Democrats pressed the Justice Department Tuesday to gather new data about the effects of so-called “stand your ground” laws on public safety.

Roughly two dozen states have adopted laws authorizing citizens to use deadly force if threatened, even if they could retreat instead.

The statutes have been the subject of intense debate since volunteer neighborhood watchman George Zimmerman fatally shot 17-year-old Trayvon Martin last year, even though Zimmerman did not rely on Florida’s stand your ground law in his defense.

President Obama and Attorney General Eric Holder have called for reconsideration of the laws and whether they encourage violence.

{mosads}Echoing those concerns, seven lawmakers issued a letter to Holder Tuesday, asking him to direct the Justice Department to adjust the definition of the term “justifiable homicide” in order to capture all cases involving stand your ground laws.

The group is also seeking data on other variables of such killings, including their location, information about who in the altercation was armed, the kind of weapons used and reasons they were justified.

“We believe this information would prove extremely useful in helping to evaluate the laws that govern the use of lethal force and in quantifying the impact of such laws on public safety and civil rights,” the lawmakers wrote to Holder.

Signatories on the letter were Sens. Dick Durbin (D-Ill.) and Mazie Hirono (D-Hawaii), along with Reps. Elijah Cummings (D-Md.), John Conyers Jr. (D-Mich.), Luis Gutiérrez (D-Ill.), Bobby Scott (D-Va.) and Marcia Fudge (D-Ohio).

The lawmakers are also asking the Justice Department to sponsor research through the National Institute of Justice related to trends in justifiable homicides and state-by-state analyses of the impacts of different variations of “stand your ground” laws.

Durbin, citing existing research, said the laws have led to increased violence.

“But the federal government does not collect adequate data on these laws’ impact,” he said. “That must change.”

While the agency has authority to research the matter, the federal government is largely powerless to stop states from passing or enforcing the laws.