The Iowa Court of Appeals on Wednesday overturned the conviction of a mother who has been imprisoned for nearly four years after being found guilty of injuring her young son, basing its decision on the boy's newfound ability to speak and claim he was hurt after sticking his arm into a washing machine.

Tammy Smith was found guilty of hurting her then-4-year-old son in 2006, after his arm was broken in four places and his shoulder dislocated. Prosecutors could not prove how the injury happened, but doctors testified it could only have been caused by a lot of force or leverage being applied to the child's arm. Smith was sentenced to 10 years in prison.

The boy was described as "developmentally delayed" and could only make grunting sounds and other noises at the time of Smith's trial. He has since been in school and met with counselors and has been able to talk about what happened, telling people he hurt his arm when he put it in a front-load washing machine that was on spin cycle.