A Frederick County has convicted a woman of first-degree murder in the stabbing of her grandmother.

The jury deliberated more than four hours before convicting 20-year-old Hestina Harris on Thursday. Prosecutors say she stabbed her grandmother, 67-year-old Lillie Morris, 20 times on Dec. 22, 2014.

Morris was found bleeding on the front lawn of the Burkittsville-area home she shared with her husband, her granddaughter and Harris' 4-month-old daughter.

Harris had told police she saw a man in a ski mask running from the house.

The Frederick News-Post reports (http://bit.ly/1RTva6v ) the trial will continue Monday to determine if Harris is criminally responsible for the slaying. Defense attorneys say they'll present evidence that mental illness rendered her not criminally responsible.

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Information from: The Frederick (Md.) News-Post, http://www.fredericknewspost.com