Gerard Marrone told the New York Daily News Thursday he resigned because of "the horrific way this boy [Leiby Kletzky] was killed."
"I have three little boys," he said. "You can't look at your kids and then look at yourself in the mirror, knowing that a little boy, who's close in age to my eldest son, was murdered so brutally."
Aron, 35, who is charged with first-degree murder and faces life in prison without the possibility of parole under New York law if convicted, still has one attorney, Pierre Bazile.
A former federal prosecutor, Morris Fodeman, told the Daily News Aron could be eligible for the federal death penalty if he took 8-year-old Leiby across state lines.
Police said they believe Aron drove the boy to an upstate New York wedding, stopping on the way at a gas station on the Palisades Parkway in New Jersey.
U.S. Attorney Loretta Lynch, in the borough of Brooklyn, declined comment, but a source said her office "has no interest" in taking on the case.
Aaron Carter is still in love with Hilary Duff
Millions of Getty images now available for free via embed tool