The mother of a mentally ill man shot by cops in his Harlem apartment said Thursday she is running out of patience with Department of Justice investigators who have examined his controversial killing for years.

The NYPD says Mohamed Bah, 28, lunged at cops with a knife in September 2012, leaving them no choice but to open fire.

Prosecutors in the office of Manhattan U.S. Attorney Preet Bharara are examining the case, but have revealed no timetable on when they will conclude their investigation into whether Bah’s civil rights were violated.

"I tell them I can wait not (much) longer for justice," Bah’s mother, Hawa Bah, said following a sit-down with prosecutors who said they're still reviewing the case.

'Knife injury' led to NYPD shooting of mentally ill man

Attorneys representing the heartbroken mother in a civil suit against the city say they’ve uncovered evidence of what they call “an execution.”

“The City of New York and New York City Police Department has done a very effective job in frankly covering up the truth of what happened with Mohamed Bah,” said attorney Debra Cohen.

The attorney with Newman Ferrara has filed a motion for sanctions against the city alleging destruction of key evidence in the case. The city, meanwhile, has asked a judge to toss the case on grounds the killing was justified.

Judge Kevin Castel has yet to rule on either request.

Family of slain man claims NYPD cops let evidence get destroyed

Earlier this month, it emerged that the lieutenant who ordered police to burst into Bah’s received a slap on the wrist from the NYPD for improperly escalating the fatal confrontation.

A spokesman for Bharara’s office declined to comment on the Bah case.