A hearing that could have meant a return behind bars for Lionel Tate, once the youngest person in modern U.S. history sentenced to life in prison, was postponed Monday because he sent a letter to a judge threatening to kill himself.

Tate, convicted at age 13 of killing a 6-year-old girl, was examined during the weekend by a psychologist whose findings will be presented at a competency hearing on Dec. 19. Broward County Circuit Judge Joel T. Lazarus, who said he received the letter Friday, decided to wait for that finding before deciding whether to revoke Tate's probation.

Tate, now 18, faces a possible return to prison for life if Lazarus finds he violated his probation. He was arrested in May on charges that he robbed a pizza delivery man at gunpoint.

Tate was 12 when he killed Tiffany Eunick, a family friend his mother was baby-sitting for, on July 28, 1999. His lawyers initially claimed the girl died accidentally while the 160-pound boy was imitating wrestling moves he saw on television, but experts said the girl died of skull fractures and a lacerated liver suffered in a beating that lasted one to five minutes.

He was convicted of first-degree murder and sentenced to life in 2001. In 2004, an appeals court tossed out the conviction after finding that it was not clear whether Tate understood what was happening to him. He pleaded guilty to second-degree murder and was sentenced to time served and 10 years' probation.

In his handwritten letter to the judge, Tate said that his public defender, H. Dohn Williams, didn't understand "my mental condition." He continued: "I stated to him before that I was hearing voices and that I wanted to kill myself."

He also quoted Florida law by statute number in saying that the judge should order a psychiatric evaluation.

Williams said outside court Monday that Tate was placed under "watch" at the county jail because of his suicidal statements.

If Tate is found incompetent, the judge could order him hospitalized or otherwise given treatment, which may prevent him from returning to jail. He was found competent to understand legal proceedings and their consequences shortly before he reached his plea agreement in January 2004.

Tate faces six charges of probation violation. The judge could sentence him to anything from life in prison to no prison time.

To many juvenile justice experts, Tate is a symbol of the difficulty that the justice system has dealing with children who commit serious crimes.

Florida and dozens of other states have laws permitting them to try children accused of serious crimes as adults, punishing them rather than seeking to rehabilitate them.

Human Rights Watch and Amnesty International reported in October that at least 2,225 people are serving life sentences without parole in U.S. prisons for crimes they committed under age 18. Six of them were 13 at the time of the crime; none was 12 as Tate was.

"We don't seem capable of recognizing that our traditional approach to crime and justice often fails with adolescents," said Jeffrey A. Butts, a research fellow at the University of Chicago's Chapin Hall Center for Children. "Prison by itself doesn't do a lot to change behavior or improve someone's chances of success."