BROWARD COUNTY, Fla. -- Attorney Ellis Rubin is petitioning the court to have his client, 19-year-old Lionel Tate, given a mental competency evaluation because he said Tate's behavior is proving that he is not competent.

Ellis' petition follows a letter that Tate sent to Judge Joel Lazarus on Tuesday. In the letter, that was sent without attorney's knowledge, Tate asked to change his plea.

On March 1, Tate pleaded guilty to the armed robbery of a pizza deliveryman last year. The plea would spare him a possible life sentence for violating probation in the 1999 killing of a 6-year-old girl.

In the letter to Lazarus Tate wrote: "Sir, it was not explained to me in great detail on what I can and cannot appeal during this plea acceptance and I would like to fight my robbery charge because I know that I can prove to you and others that I did not commit these crimes I am being charged with." (Full Story)

Tate previously admitted that he had violated probation by possessing a gun during the May 23, 2005, robbery -- and even without a conviction in the robbery, he could face life in prison for that admission.

The request for the mental evaluation is the latest twist in the long-running case of Tate, who was convicted of killing Tiffany Eunick when he was only 12. He was the youngest person in modern U.S. history to receive a life sentence.

The court will complete an evaluation of Tate's mental competency within the next two weeks.