WASHINGTON — More than a half-century after 14-year-old Emmett Till was brutally murdered after whistling at a white woman in Money, Mississippi, a promise to his mother has been kept.

Legislation signed into law this week authorizes new offices in the U.S. Department of Justice and FBI to investigate long forgotten, racially motivated killings, such as the unsolved case of the teenager.

The initiative, ushered through the House by U.S. Rep. John Lewis, D-Atlanta last year, recently won approval in the Senate, largely through the persistence of Alvin Sykes, a self-educated victims’ rights advocate. Sykes promised Mamie Till-Mobley, when she was on her deathbed six years ago, that he would pursue her son’s case.

He formed the Emmett Till Justice Campaign in 2003, and the group later sought help from Lewis, himself a veteran of the civil rights movement.

“It would not have happened without John Lewis,” said Sykes, who lives in Kansas City, Mo.

Even so, the 52-year-old activist had to overcome a major obstacle when Sen. Tom Coburn, an Oklahoma Republican, placed a “hold” on the Emmett Till Unsolved Civil Rights Crime Act among dozens of other measures involved in a budget dispute.

With Congress moving toward adjournment and the bill in danger of dying, Sykes flew to Washington to make a personal plea to Coburn, who ultimately was persuaded to lift his hold and allow the measure to pass Sept. 23 by unanimous consent. The earlier vote in the House had been 422-2, with Republican Reps. Lynn Westmoreland of Grantville, Ga., and Ron Paul of Texas voting no.

President Bush signed the bill into law Tuesday without ceremony, a minor disappointment for Sykes, who had hoped for a public signing. However, the advocate was already making plans for the next step.

“I’ll be happy when I start seeing the prosecutions,” he said of the program, which will need $13.5 million in congressional appropriations a year. The cases targeted are murders, occurring before 1970, in which suspects are thought to be alive.

How many cases will be investigated is unknown, Sykes said. He said the FBI already has 26 cases “in various stages of investigation.”

The program will include searching for more examples through a community outreach effort in cities such as Detroit and Chicago, where black families sometimes fled in response to racial violence in the South.

A statement released by the office of Rep. Lewis said the congressman was “confident that this new law will bring healing, justice, and peace to affected families, friends, communities, and our nation as a whole.”