MIAMI -

The key prosecution witness in the case of a South Florida woman accused of killing missing Florida foster child Rilya Wilson remained on the stand Thursday.

Jailhouse informant Robin Lunceford continued to undergo cross-examination by an attorney for 66-year-old Geralyn Graham. The defense is trying to poke holes in Lunceford's story that Graham confessed while the two shared a jail cell to smothering 4-year-old Rilya with a pillow and burying her body near water. The body was never found.

"I was tired. I wanted to be left alone. I just wanted to do the right thing and leave me alone and it never stopped," said Lunceford as she discussed abuse she suffered by fellow inmates and corrections officers after reporting Graham had confessed to the murder.

On Thursday, defense attorneys produced profane letters written by Lunceford, who threatened to withdraw her testimony unless her conditions in jail were improved. Lunceford had her life sentence cut to 10 years in return for her testimony.

She defended her actions, saying she did it because of the abuse she suffered in jail.

"After so much abuse and so much people talking s***, I finally said, 'F*** everybody,' and I put her picture on my tag and if they didn't like it, they could just kick my a**, I'd kick theirs. I'm going to get on this stand," said Lunceford.

A television interview of Lunceford was also played in court.

Graham faces life in prison if convicted of murder, kidnapping and child abuse charges. Graham claims Rilya was taken from her home for mental tests by a state worker in 2001 and never returned. Investigators say no evidence backs up Graham's story.

The trial is expected to last several more weeks.