A judge in Phoenix dismissed the murder case against Berlin-born Arizona woman Debra Milke, who spent more than 20 years on death row for the killing of her four-year-old son in 1989.

Milke, the daughter of an German mother and an American man, sobbed and hugged her supporters. Judge Rosa Mroz ended the case after prosecutors lost their final appeal last week.

Christopher was four years old when he was shot. He thought he was going to see Santa Claus at a mall in December 1989. But he was taken to a desert near Phoenix by two men instead and shot three times in the head.

Milke was sentenced to death in 1991. Prosecutors and police believe she hired two men to kidnap her son and to kill him. The US court assumed Milke wanted to get rid of the boy and get money from the insurance. However, no evidence was found to prove this assumption.

To this day, a motive for this murder remains unknown. Nevertheless, the prosecutors still believe that she didn't want the child, but also didn't want to let him live with his father.

In 2013, Milke's conviction and death sentence were thrown out by a federal appeals court, which said the original prosecutor failed to rebeal evidence that could have helped her challenge a detective, who said she had confessed to him.

Furthermore, Milke's conviction was entirely based on her confession given to the now-discredited detective. The US court believed that the prosecutors knew about Phoenix police Detective Armando Saldate's record of misconduct, in other cases, but decided to ignore it.

Christopher's mother has maintained her innocence and denied that she confessed to the killing.

Two men responsible for the murder of the four-year-old boy were also sentenced to death and are still waiting for execution. During the long trial process, they never testified against the mother.

jil/jr (AP, dpa)