Brooklyn federal prosecutors are joining a lawsuit into the purging of 117,000 names from the voter rolls. View Full Caption DNAinfo/Carolina Pichardo

BROOKLYN — The U.S. Attorney's office is jumping into a federal lawsuit over the purging of 117,000 voter names by the city Board of Elections Brooklyn office, according to a letter filed with the court Thursday.

Federal civil rights prosecutors told Judge Nicholas Garaufis that their office had been investigating voter suppression in Brooklyn since suspended-Chief Clerk Diane Haslett-Rudiano was accused in April 2016 of kicking out more than a 100,000 active voters while reportedly doing a routine update to eliminate dead people and those who had moved away.

Good government group Common Cause sued the city BOE claiming the Brooklyn borough office violated the National Voter Rights Act by deleting the names of active voters.

"Federal law demands careful maintenance of the voter rolls to ensure lists are kept accurate, without unjustifiably and unlawfully purging eligible citizens,” said Principal Deputy Assistant Attorney General Vanita Gupta, head of the Justice Department’s Civil Rights Division.

“The department appreciates the continued cooperation of the New York City Board of Elections, including proactive steps taken to start remedying violations that have occurred — but more is necessary to reach full compliance with the law."

Voters across the city ran into problems casting ballots despite assurances from the BOE that they were ready for the primary.

An entire block of Clinton Hill voters were deleted from the list of eligible voters in the purge. Residents showed up to P.S. 11 on Waverly Avenue on April 19, 2016 to vote and were forced to cast their votes on affidavits, poll workers told DNAinfo New York at the time.

John Philip, 45, who said he'd voted at the school for the last 14 years, was not in the voting books and neither was his wife.

"It’s a little frustrating, I want to make sure there’s accountability," Philip said at the time. "I don't know what the board has planned to put people’s minds at ease for long-term registered Democrats to know their vote was counted."