The suspect held in connection with killing and dismemberment of Levi Aron, the 8-year-old Brooklyn boy Leiby Kletzky, pleaded not guilty on Thursday. According to defense attorneys, he will undergo a psychiatric examination since he claimed that he hears voices and suffers hallucinations.

I have some serious concerns about the client's mental state, his cognitive ability. He's indicated to me that he hears voices and there's some hallucinations involved, as well, said Pierre Bazile, one of Aron's defense attorneys, according to NY1 report.

Aron, 35, had admitted to smothering, killing and dismembering the Borough Park boy, the Brooklyn district attorney told the judge.

Leiby Kletzky was reported missing on Monday evening after he failed to return home from day camp. Surveillance video was used by detectives to identify Aron as a suspect in the kid's disappearance.

Leiby's dismembered body parts were found in Aron's refrigerator when the police searched his apartment on Wednesday.

We have concerns with his mental state. He does appear to be unwell, said Bazile. We're going to have him examined.

For now, the most important thing is to have him examined psychologically, said Gerard Marrone, another defense attorney. It's called a 730 examination. So he's remanded at this time. We'll see what his psychological state is and that's the most important thing right now to everyone involved, according to NY1 report.

Police Commissioner Ray Kelly said, that Aron wrote a confession about killing and dismembering Leiby's body and the medical examiner has reasons to believe that Leiby may have been smothered or suffocated. Lab tests are yet to determine the exact cause of death.

According to Kelly, the boy's arms and wrists have marks that make it evident that the boy was tied up, but there are no signs of sexual molestation.

Brooklyn District Attorney Charles Hynes said a grand jury is currently reviewing the evidence against Aron.

Right now the jury is hearing the testimony. I expect that the testimony should be concluded by tomorrow, and then we will ask for the main charge of felony murder, based on the kidnapping, which is murder in the first degree, and whatever other charges we think are sustainable, said Hynes.

Aron is scheduled to be back in court in two weeks, the report said.