TAMPA, Fla. -- Incriminating statements made in custody by the man accused of killing 13-year-old Sarah Michelle Lunde two years ago should be thrown out of court because investigators continued to illegally question and "manipulate" him after he asked for a lawyer, his attorney argued in a hearing Wednesday.

Lacking solid physical evidence linking David Lee Onstott to Sarah's April 2005 slaying, prosecutors want to use statements made by Onstott while in custody to investigators, his mother and a fellow jail inmate to try to convict him at trial next month.

But his attorney, John Skye, told state Circuit Judge Ronald N. Ficarrotta that anything Onstott told investigators or that they heard is inadmissible because they illegally continued to interrogate him after he invoked his right to a lawyer. They say he eventually made statements that amounted to confessions.

Skye also contends that investigators illegally listened in and recorded a conversation between Onstott and his mother the day Lunde's body was found and that they coerced her to get him to talk about what happened.

"Mr. Onstott and his mother were led to believe that their conversation was going to be private," Skye told the judge.

Skye also has challenged the strategy investigators used to keep Onstott in custody and the use of a confidential informant in the jail to ply him about Sarah's disappearance.

Prosecutors say investigators did nothing wrong and that Onstott was allowed to talk to his attorney on a cell phone at one point while he was in custody.

The statements are key to prosecutors' case since there is no physical or forensic evidence that ties Onstott to the death of Sarah, whose slaying came on the heels of the high-profile abduction and slaying of 9-year-old Jessica Lunsford in Citrus County.

Sarah's mother, Kelly May, who watched Wednesday's proceedings, said she wasn't overly concerned that the confessions could be thrown out.

"The only concern I have is that he won't get the death penalty, but he's an animal who needs to be locked away," May said.

She said it was the first time she had seen Onstott since Sarah was killed. He sat across the courtroom, dressed in an orange jail jumpsuit with ankles chained.

"It's been a long, hard two years," May said. "Sarah is gone and she's not coming back. My purpose for being here is to make sure she gets the justice she deserves."

The massive, weeklong search for Sarah captured the nation's attention before her partially clothed body was found in an abandoned fish pond near her family's mobile home in Ruskin, south of Tampa, on April 16, 2005, a week after she was last seen.

Authorities said Onstott confessed to strangling Sarah after showing up at the family's home early one morning looking for May, whom he had once dated.

Sarah's older brother came home later and found the front door wide open and his sister gone, but the family initially assumed Sarah had gone to a friend's house. She was not reported missing until two days later.

Prosecutors are seeking the death penalty for Onstott, who has pleaded not guilty to first-degree murder and attempted sexual battery.

The hearing resumes Thursday.