"I think it is reasonable to say it was based on marks on the defendant that there was some struggle," NYPD Commissioner Ray Kelly said.
Leiby Kletzky vanished late Monday afternoon after getting lost during what was supposed to have been a seven-block walk from his day camp to a meeting spot with his mother.
Investigators later used a surveillance video to trace the missing boy to Levi Aron, a hardware supply store clerk the boy had apparently asked for directions.
Kelly said the victim may have been restrained while being held in the suspect's apartment.
He added that Aron went into some graphic detail during his confession as to how the boy died and after the boy died. Detectives found the boy's severed feet wrapped in plastic in the man's freezer, as well as a cutting board and three bloody carving knives. A plastic garbage bag with bloody towels was nearby.
A preliminary medical examination indicates Leiby Kletzky was "smothered or suffocated," but it remained unclear when that happened, Kelly said.
Kelly said Aron ended his written confession with, "I'm sorry for the hurt that I caused."
Beyond that, "he hasn't expressed any remorse," Kelly said.
In court on Thursday, Aron's lawyer Pierre Bazile told a judge that his client told him that he hears voices and he has had hallucinations.
Aron pleaded not guilty to first-degree murder and kidnapping charges. A judge ordered a psychological evaluation.
Aron entered a Brooklyn courtroom for the arraignment looking disheveled and pale.
As he was led out from the courthouse holding pens, other inmates screamed obscenities at him.
"From the Aron family, they'd like to extend their condolences to the family of the boy," Bazille said earlier, adding they would let the justice system work and would not make any further statements.
Kelly said the suspect denied molesting his victim, but that "laboratory tests still being conducted that may possibly disprove that. That is to be determined."
He said investigators are unsure if the boy was killed Monday night or Tuesday night, as stated in the confession. They are also unsure if he took the victim to a wedding in New Square, Rockland County Monday night, as also stated in the confession.
"In the statement, (Aron) goes through finding the boy on the street, that he was lost, he asked him to take him to a book store, couldn't find the book store, then asked him if he wanted to go to the wedding, took him on a ride to the wedding, brought him back," Kelly said.
Aron spent several hours at the wedding on Monday night, Kelly said. Detectives have been reviewing videotape from a wedding reception and interviewing guests, but he remained unclear whether the boy was with him.
Aron told police he killed the child Tuesday in a panic after learning that a massive search was under way.
Brooklyn District Attorney Charles Hays said he plans to charge Aron with felony murder, and was also investigating whether he might have had any improper contact with children in the past.
Three computers have been recovered from the suspect's house, and they are being examined. Police are also searching the house for more evidence. There is no evidence at this point that the suspect stalked children in the past, Kelly said.
Thousands of mourners gathered in Brooklyn on Wednesday evening for the boy's funeral.
The Wednesday night service, held in an outdoor courtyard, drew a sea of men in black hats and coats and women in modest dresses - the traditional dress of the Hasidic Jews who call the neighborhood home. The overflow crowd packed neighboring streets to listen to the ceremony in Yiddish and Hebrew.
The funeral came just hours after police discovered Leiby's remains.
Leiby disappeared Monday afternoon while on his way to meet his mother on a street corner seven blocks from his day camp, the first time the young Hasidic child was allowed to walk the route alone. Authorities said he had evidently gotten lost after missing a turn, and had reached out to Aron, a stranger, for help.
The gruesome killing shocked the tight-knit Hasidic community in Borough Park, in part because it is one of the safest sections of the city and because Aron is himself an Orthodox Jew, although not Hasidic. The Hasidim are ultra-Orthodox Jews.
"This is a no-crime area," said state Assemblyman Dov Hikind, whose district includes the area. "Everybody is absolutely horrified," he said.
While the medical examiner's office said it was still investigating how the boy was killed, the body was released so that the boy could be buried Wednesday evening according to Jewish custom.
Speakers at the funeral stressed the community's resilience and unity after what one called an unnatural death.
"This is not human," said Moses Klein, 73, a retired caterer who lives near the corner where the boy was last seen.
The break in the case came when investigators watched a grainy video that showed the boy, wearing his backpack, getting into a car with a man outside a dentist's office. Detectives tracked the dentist down at his home in New Jersey, and he remembered someone coming to pay a bill. Police identified Aron using records from the office, and 40 minutes later he was arrested, shortly before 3 a.m. Wednesday.
Aron told police where to find the rest of the body; it was in pieces, wrapped in plastic bags, inside a red suitcase that had been tossed into a trash bin in another Brooklyn neighborhood, Kelly said.
Police said there was no evidence the boy was sexually assaulted, but they would not otherwise shed any light on a motive except to say Aron told them he "panicked" when he saw photos of the missing boy on fliers that were distributed in the neighborhood. Police were looking into whether Aron had a history of mental illness.
Police said Aron, who is divorced, lives alone in an attic in a building shared with his father and uncle.
Kelly said it was "totally random" that Aron grabbed the boy, and aside from a summons for urinating in public, he had no criminal record.
He lived most of his life in New York and worked as a clerk at a hardware supply store around the corner from his home, authorities said. Co-workers said Aron was at work on Tuesday.
"He seemed a little troubled," said employee Chamin Kramer, who added Aron usually came and went quietly.
Aron lived briefly in Memphis, Tenn., and his ex-wife, Deborah Aron, still lives in the area. She said he never showed signs of violence toward her two children from a previous relationship.
"It's utter disbelief," she said from the toy-littered backyard of her home in the Memphis suburb of Germantown. "This ain't the Levi I know." Deborah Aron said the couple divorced about four years ago after a year of marriage. She described Levi Aron as a person who was shy until he got to know you and said he enjoyed music, karaoke and "American Idol." She said he attended Orthodox Jewish services in Memphis.
He was "more of a mother's boy than a father's boy," who lived at home until he met her, she said.
She said Levi injured his head when he was hit by a car while riding his bike at the age of 9 and suffered problems stemming from that accident.
Some information from The Associated Press.
For more information on The New York Society for the Prevention of Cruelty to Children, please visit: NYSPCC.org