SYRACUSE -- A 21-year-old woman on Wednesday denied trying to kill herself or writing the suicide note that has become a key piece of evidence in the murder trial of her mother.

Wiping away tears with a tissue, Ashley Wallace told an Onondaga County Court jury that she did not fatally poison her father or stepfather as defense lawyers have tried to suggest.

"Did you, when you were 12 years old, poison your father with antifreeze and rat poison?" District Attorney William Fitzpatrick asked bluntly.

"No, I did not," Wallace replied.

"Did you poison your stepfather with antifreeze in 2005?" the prosecutor asked.

"No, I did not," Wallace replied.

Wallace was the first witness in the trial of Stacey Castor, 41, of Clay, who is charged with killing her husband David Castor in August 2005. She's also accused of trying to kill Wallace with an overdose of drugs and alcohol in September 2007 and faces an attempted murder charge.

Prosecutors contend Castor concocted a suicide scenario to frame her daughter for the two deaths.

On Sept. 12, the night before her alleged overdose, Wallace said she had drank several wine coolers with her mother, who also gave her Tylenol with codeine and sleeping pills. Wallace said the first wine cooler had a bitter taste.

Wallace described how her mother invited her to get drunk on Sept. 13 after Castor picked Wallace up at school that morning. The day before, detectives had visited Wallace at school to ask her questions about Michael Wallace's death in January 2000.

Castor told her that it had been a rough week and she wanted to celebrate her daughter's upcoming 21st birthday in case she wasn't around when the day arrived, Wallace said. They bought vodka, Sprite and orange juice and took it home, where Castor mixed the drinks.

"I took a drink and it tasted horrible. It was hurting my stomach," she said.

Castor said it was just too much vodka and showed Wallace how to consume her drink from a straw so she wouldn't have to taste it, Wallace testified.

Asked why she kept drinking, Wallace said, "because I trusted her (Castor)."

"I didn't feel good at all. I felt like I was sitting in a tunnel. All I could see was what was in front of me. I felt tired," said Wallace. "The next thing I know I was waking up in the hospital and detectives were asking me what I did ... about the note.

"I didn't know what they were talking about. I didn't write any note. I didn't take anything," Wallace said.

Wallace denied knowing anything about the computer-generated suicide note that was purportedly written by her as a deathbed confession to the two murders. Prosecutors contend it was Castor who composed the 700-word note.

"I'm 100 percent positive that I did not write that note," Wallace told Fitzpatrick as he showed her a copy of it in the courtroom.

Defense attorney Charles Keller cross-examined Wallace for nearly 90 minutes, focusing on discrepancies between her testimony Wednesday and the statements she gave previously to a grand jury and to investigators, including how many wine coolers she had on Sept. 12, what kind of pills her mother gave her and when she took them, and when Stacey Castor first told her that Michael Wallace had died from poisoning.

Keller also tried to portray Wallace as having sour relationships with her father and David Castor. Keller has suggested from the beginning of the case that Wallace is the killer of the two men.

Near the end of the his questioning, Wallace admitted to Keller that she wrote a letter in 2005 to an ex-boyfriend in which she said she had considered suicide twice previously.

But Fitzpatrick finished by asking her about the letter. Wallace said she had been recalling the depression she felt in 2000 following her father's death and never attempted to carry out any actions.

David Castor's death was initially ruled a suicide but investigators later determined he was poisoned with ethylene glycol, a toxic chemical found in antifreeze, and arrested Castor in September 2007.

After David Castor died, investigators in neighboring Cayuga County exhumed Wallace's body. Doctors originally ruled that the 38-year-old Wallace died from a heart attack, but after the exhumation authorities ruled his death a homicide caused by ingesting ethylene glycol.

Although Castor has not been charged with killing Michael Wallace, Fitzpatrick has presented evidence of Wallace's poisoning as proof she killed David Castor in a similar fashion.

If convicted, Castor could face a maximum of 25 years on the second-degree murder charge. She also could face a consecutive sentence of 25 years if convicted of attempted second-degree murder.