A New York judge declared a mistrial in the murder case of a six-year-old boy who went missing in 1979 after the jury could not reach a verdict.
More than 30 years after Etan Patz disappeared, defendant Pedro Hernandez confessed in 2012 to killing the boy.
But Mr Hernandez's lawyers say the confession was false and claim he is mentally ill.
Mr Hernandez will remain in jail as prosecutors set a new trial date.
Etan's father, Stanley Patz, expressed his frustration over the jury's inability to decide but added, "I think we have closure already".
Etan's disappearance was one of most prominent missing person cases during the 1980s. He was the first missing child to appear on milk cartons.
The boy vanished in 1979 while walking to a school bus stop on his own for the first time.
Mr Hernandez was a teenager who moved from Manhattan to New Jersey at the time when detectives were frantically searching the streets for the missing first grader.
In 2012, Mr Hernandez admitted to choking the boy in the basement of the shop where he worked, putting the body in a bag, putting the bag in a banana box and eventually dumping the body about two blocks away from the store.
But Etan's body was never found, and no physical evidence was uncovered to link Mr Hernandez to the crime.
Defence lawyer Harvey Fishbein said during closing arguments: "Pedro Hernandez is the only witness against himself...the stories he told over the years, including in 2012, and since, are the only evidence. Yet he is inconsistent and unreliable.''
Hernandez's lawyers pointed to another suspect Jose Ramos, a convicted paedophile.
According to a former prison informant with whom lawyers were working, Ramos claimed he was with Etan the day the boy vanished and admitted to molesting the child.
During 18 days of deliberations, the jury was deadlocked three times before the judge declared the mistrial.
District Attorney Cyrus Vance on Friday thanked the Patz family for their "courage and determination" over the years.
"The challenges in this case were exacerbated by the passage of time, but they should not, and did not, deter us," Mr Vance said.
