Phoenix police are asking anyone with information to come forward. Health privacy laws prevent them from releasing their names.
The 11-yearold girl authorities are only calling Emily had been receiving chemotherapy at Phoenix Children's Hospital for about a month.
Phoenix police Sgt. Steve Martos says an infection forced doctors to amputate her right arm and insert a heart catheter. The device was set to be taken out before her mother removed an IV from the girl and walked her out of the hospital Wednesday night.
Martos says the catheter could cause a deadly infection