"Look, everybody knows when blood relations have offspring, there can be genetic defects," Howard Greenberg, the attorney for suspect Levi Aron, said Wednesday.
Aron, 35, is accused of kidnapping 8-year-old Leiby off a Borough Park street in July, then killing and dismembering him.
"It's something that needs to be investigated down to the ground," Greenberg said. "[Aron] suffered a severe head injury as a young man. There's a history of schizophrenia. There's inbreeding in that community."
Greenberg's remarks prompted an angry reaction in the Orthodox Jewish community, the New York Post reported.
Assemblyman Dov Hikind called Greenberg "sick" and "pathetic."
"This lawyer is simply out of his freaking mind," Hikind said. "He's a sick, self-hating Jew who's making a mockery of this case. It's insulting and degrading to our entire community."