Beverley Allitt - In 1991, the British nurse murdered four children and injured five others by injecting them with insulin or potassium, causing cardiac arrest. Allitt was sentenced to a minimum of 30 years in prison. Stella Maudine Nickell - In 1986, the Seattle-based nurse poisoned her husband and an innocent shopper by planting cyanide-laced pain-relief capsules on drug store shelves in an intricate plan to cash in her husband's life insurance policies. Nickell is serving a 90-year sentence. Kathleen Folbigg - On a killing spree that lasted from 1989 until 1999, the Australian serial killer murdered four of her children by suffocating them. She is serving a 30-year sentence.