Levi Aron, 36, entered a plea of guilty in a New York court that will put him behind bars for at least 40 years, The New York Times reported. He could have been sentenced to life if he was convicted at trial.
While Aron's lawyers had been considering an insanity defense, Judge Neil Firetog said during Thursday's hearing that would "not be a viable defense." Investigators said they found antipsychotic medication in Aron's apartment last summer.
Leiby, who was about to celebrate his 10th birthday, disappeared on the day he was allowed to walk part of the way home from camp on his own. He apparently became lost and asked directions from Aron.
Aron said he took Leiby to a wedding in Rockland County and then returned with the boy to his apartment in Brooklyn's Kensington neighborhood. He said he became scared when he learned that police and members of the community of Hasidic Jews in Borough Park had launched a search for the boy. Aron said he smothered the child and cut up the body.
Police found body parts in a suitcase left in a trashcan more than 2 miles away and others in Aron's freezer.
Notable deaths of 2014 [PHOTOS]