A Johnston man has been found guilty of killing his girlfriend, then dismembering her and trying to burn her remains in his fireplace. Donald Greenslit was found guilty Monday in Providence Superior Court of first-degree murder and other charges. The jury began deliberating Friday in the killing of Stacie Dorego, 39, in January 2012. She was Greenslit’s girlfriend and the mother of his two children. Her killing was discovered after someone reported to authorities that smoke was coming from Greenslit’s home. Authorities say they found Dorego’s burned remains in a fireplace and the children, ages 3 and 5, sitting in a bedroom and coughing from the smoke.