A woman who spent 22 years on death row before her conviction was thrown out says her release is "bittersweet" because she still does not know why her four-year-old son was murdered. Debra Milke spoke yesterday, a day after a judge cleared her of any part in the 1989 killing of her son Christopher, who thought he was going to see Santa Claus when he was taken to the Arizona desert and shot by two men who are now in prison for his death.Milke again steadfastly denied involvement and responded quickly when told that prosecutors still think she had a part in it."Based on what?" she asked.It was the first time Milke has spoken publicly at length since a federal appeals court overturned her conviction two years ago. The appellate court found prosecutors had failed to disclose a history of misconduct by the lead investigator in the case, Phoenix police detective Armando Saldate.The misconduct included multiple court rulings in other cases that Saldate had either lied under oath or violated suspects' rights during interrogations.The case rested largely on Milke's purported confession to Saldate, who did not record the interrogation. Milke, now 51, disputed that she had confessed.Prosecutors sought to retry Milke but Arizona's highest court rejected that bid last week, leading to the dismissal of the case.Maricopa County Attorney Bill Montgomery said he was confident that his office could have won another conviction regardless of questions about Saldate's credibility. He said numerous other witnesses would have testified about incriminating comments made by Milke at the time."I have seen nothing in reviewing the entire trial transcript, or anything that has been brought up since, that would cause me to question the decision of the jury when she was first convicted," he said.At a news conference yesterday Milke's voice cracked with emotion as she read a statement saying she had suffered two tragedies - the death of her child and the detective's false claim that she had confessed to killing the boy.Asked about a box of ammunition police found in her handbag when they first spoke to her, which was of the same calibre as that used to kill the child, she said she found the bullets in a roommate's clothes while laundering."Clearly, I forgot they were in my purse." ..